Putting on Tefillin in middle of Davening:
What is one to do if his Tefillin arrived in middle of Davening, or if he forgot to put on Tefillin and remembered in middle of Davening? May he wear the Tefillin and may a blesisng be recited? The same question applies to one who used the bathroom in middle of Davening and now desires to re-wear his Tefillin, may he do so and may a new blessing be said [if he had a bowel movement]? Practically, this depends on the area of Davening that he is currently holding.
During Pesukei Dezimra: One may not recite a blessing on Tefillin between Az Yashir and Yishtabach. Likewise, one may not recite a blessing on Tefillin in middle of Pesukei Dezimra [even Bein Haperakim, and certainly not in middle of a Perek]. However one may recite a blessing over the Tefillin between Yishtabach and Yotzer. [Thus in the event that one received Tefillin, or remembered to put on Tefillin, in middle of Pesukei Dezimra, one is to place them on without a blessing, and between Yishtabach and Yotzer is to shake them and recite a blessing.]
Between Birchas Shema and start of Shema: If one remembered to put on Tefillin, or received Tefillin, after beginning the blessing of Yotzer Or but before Shema, he may place it on with a blessing between the Perakim [which is between Yotzer Hameoros and Ahavas Olam, and Ahavas Olam and Shema] although not in the midst of the paragraph. [However, he may place it on in middle of the paragraph without a blessing and then recite a blesisng between the paragraphs.]
Between start of Shema and Goal Yisrael: If one received Tefillin in middle of Shema or after Shema but before saying Goal Yisrael, one may place it on with a blessing even in middle of the paragraph. [This applies even if one already read Shema prior to Davening to fulfill one’s obligation, and is now reading it.]
In the event that one received Tefillin, or remembered to put on Tefillin, in middle of Pesukei Dezimra, one is to place them on without a blessing, and between Yishtabach and Yotzer he is to shake them and recite a blessing. If one remembered to put on Tefillin, or received Tefillin, after beginning the blessing of Yotzer Or but before Shema, he may place it on with a blessing between the Perakim [which is between Yotzer Hameoros and Ahavas Olam, and Ahavas Olam and Shema] although not in the midst of the paragraph. If one received Tefillin in middle of Shema or afterwards, from Veahavta and onwards, one may place it on with a blessing even in middle of the paragraph. Between Geula and Tefila one may not say a blessing on the Tefillin. Rather, one is to wear it without a blessing.
Summary: False testimony-The relationship of Shema and Tefillin:
One who says Shema without Tefillin is considered to testify falsely. The Poskim imply that this applies even if one plans to wear Tefillin later on after saying Shema. Nonetheless, practically the custom is to allow saying Shema without Tefillin so long as one plans to wear it later on in the day, as it is only considered false testimony if one does not plan to wear Tefillin at all that day. Even according to the former approach, this prohibition only applies to when one is reciting Shema for the purpose of fulfilling his obligation. If however he is simply reciting it to read from the Torah, there is no obligation to wear Tefillin. However some were stringent even in such a case. From some Poskim it is evident that this law applies also to the Tefillin; just as one may not say Shema without Tefillin so too one may not wear Tefillin without saying Shema.
 Ketzos Hashulchan 18/6
 Admur 53/3 and Michaber 53/3 regarding a Tallis [between Az Yahsir and Yishtabach] and the Elya Raba and M”B 53/6 rules the same applies regarding Tefillin; Ketzos Hashulchan 18/6
 Ketzos Hashulchan 18 footnote 23 based on the wording in Admur here “As it is forbidden to make an interval between Baruch Sheamar and Yishtabach”;
 So rules regarding Tallis: Admur ibid; Chayeh Adam 20/3; Gloss of Rav Akiva Eiger ibid; Kitzur SHU”A 14/8; Kaf Hachaim 53/7
The reason: As it is forbidden to make an interval between Baruch Sheamar and Yishtabach even if it is for the sake of a Mitzvah, as explained in 51/4. [ibid] Now although it is permitted to wear Tefillin with a blessing even in the middle of Birchas Shema [see 66/3 and 11], nevertheless this is because it is an obligation to read Shema and Daven Shemoneh Esrei wearing Tefillin. However there is no obligation to say Pesukei Dezimra wearing Tefillin, and hence one must delay the blessing until after Yishtabach. [Ketzos Hashulchan ibid footnote 24; Kaf Hachaim 53/7]
Other opinions: Some Poskim rule one may put on the Tefillin with a blessing even in middle of the Perek, and certainly between the Perakim in Pesukei Dezimra. [Birkeiy Yosef 53/4; Magen Giborim based on Teshuvas Harambam 147; Chayeh Adam 20/3; M”B 53/6; Yabia Omer 9/82] However even according to them one may not do so between Az Yashir and Yishtabach. [Michaber ibid]
 The reason: As it is permitted to make an interval in that area for the sake of a Mitzvah, as explained in 54/3 [ibid]
 Piskeiy Teshuvos 53 footnote 14; See Admur 66/3; Michaber 66/2
Other opinions: Some Poskim rule that in the event that one had Tefillin beforehand and simply forgot to wear them, it is forbidden to put them on during Pesukei Dezimra, or even between Yishtabach and Barchu, even without a blessing. [M”B 53/7]
 Chayeh Adam 20, brought in Ketzos Hashulchan ibid; Hefsek Betefila 5/2-5 [p. 86]; See Admur 66/11 in first opinion
 Admur 66/3; Ketzos Hashulchan 19/4 in name of Derech Hachaim and implication of Admur 66/11, Vetzaruch Iyun as to why the Ketzos Hashulchan omitted 66/3 in which Admur explicitly mentions this ruling
The reason: As Tefillin is an obligation to wear for Shema and Shemoneh Esrei in order to accept the complete Yoke of Heaven. [66/3 and 11]
 M”B 54/13
 Siddur Admur; second and main opinion in 66/11; Tur; Hagahos Maimanis; M”B 66/15
Other opinions-Ruling of Admur in his Shulchan Aruch: In 66/11 Admur records a dispute in this matter. Some Poskim [Ram Mekotzi Tosafus Brachos 14b; Kuntrus Achron 66/2] rule one may only place the Tefillin on with a blessing between the Perakim, while in middle of the Perek a blessing may not be said. Thus from Vayomer and onwards one is to wear the Tefillin without a blessing and then after Shemoneh Esrei he is to touch the Tefillin and say a blessing. Other Poskim [Tur; Hagahos Maimanis; Kuntrus Achron 66/3] however rule one may say a blessing even in middle of the Perek. Practically Admur concludes that one is to follow the latter opinion. [ibid] Other Poskim rule like the first opinion, that a blesisng may only be recited between the Perakim, and hence from Vayomer and onwards one can no longer say a blesisng until after Shemoneh esrei. [Kaf Hachaim 66/15]
 The reason: As Tefillin is an obligation to wear for Shema and Shemoneh Esrei in order to accept the complete Yoke of Heaven. [66/3 and 11] One is required to recite every word of Shema with his Tefillin, and hence one cannot wait until between the Perkaim. [M”B ibid; Ketzos Hashulchan 18 footnote 12]
 P”M 66 M”Z 2; Unlike Piskeiy Teshuvos 66 footnote 33 in name of Orchos Chaim 66/13
 66/11; Siddur Admur; Rama 66/8
The reason: As it has the same law as the Shemoneh Esrei itself. Even regarding answering Kaddish or Kedusha, which is a Mitzvah Overes [is forbidden between Goal Yisrael and Shemoneh Esrei]. Thus certainly one may not recite a blessing over the Tefillin which can technically be recited afterwards. Practcially, this is the custom that one is to follow. [ibid]
 Siddur Admur; Implication of 66/11; Rama 66/8
The reason: Although even putting the Tallis without a blessing is considered an interval between Geula and Tefila, being that the Tallis does not have such a need for the Tefila nevertheless it is permitted to put on Tefillin between Geula and Tefila because Tefillin is an obligation to wear during Davening in order to accept the complete yoke of heaven. However Tzitzis is not an obligation of the body to wear unless one is wearing a Tallis that is obligated in Tzitzis. [66/11]
 Admur 25/1; Tur 25; Brachos 14b
The reason: As he recites “Ukeshartem Leos” and he is not doing so. [Admur ibid; Levush 25/1; Talmidei Rabbeinu Yona Brachos ibid] Alternatively, The reason is as follows: Tefillin contain the Parshiyos of Shema. The Tefillin draw down a Makif level of G-dliness from these Parshiyos while the actual reading of Shema takes this Makif and draws it down internally into one’s soul. It is for this reason that one needs to first wear the Tefillin and only afterwards recite Shema, as one cannot draw down the internal Hamshacha from the Makif if he has not yet drawn down the Makif. This is why it is considered false testimony for one to say Shema without the Tefillin [Torah Or Vayakhel]
 Admur 66/11 rules that it is better to Daven in private with Tefillin than to Daven with a Minyan but without Tefillin due to Eidus Sheker. Likewise, he implies that it one is not to say Shema without Tefillin unless the time of Shema is passing. From here we learn that saying Shema without Tefillin is Eidus Sheker even if he plans to wear Tefillin later on and say Shema again while wearing them. So is also proven from Torah Or Vayakhel in that one cannot draw down the Penimi without first having worn Tefillin and drawing down the Makif. Now, Admur 58/4-5 makes it evident that this refers only when reading Shema after sunrise as in 58/4 he permits reading Shema before sunrise without Tefillin while in 58/5 he writes that if it is after sunrise one is to read Shema as soon as possible with Tallis and Tefillin. Vetzaruch Iyun as to the difference between before and after sunrise, that before sunrise it may be said without Tefillin and after sunrise it may not! Perhaps then one must say this entire law of Admur refers to one who does not have time or ability or desire to wear them before sunrise, although ideally he should do so. Vetzaruch Iyun!
 The reason: As a) One has said “Ukishartem” and has not yet done so. B) One can’t draw down the Mkaif prior to the Penimi.
 Os Chaim 25/6; Rebbe in Toras Menachem 28th Sivan 1952;
The reason: It is not considered false testimony to say the morning Shema prior to prayer, without Tefillin, as one will wear Tefillin later on. [Rebbe in Toras Menachem 28th Sivan 1952]
 Degul Merivava and Rav Akiva Eiger, brought in M”B 46/33; Binyan Olam 7; Kaf Hachaim 25/27; Rebbe in Toras Menachem 28th Sivan 1952
 Minhag Hageonim to wear Tefillin during Shema of Maariv, brought in Hagahos Maimanis on Rambam Tefillin 4 in name of Baal Haittur, brought in Beis Yosef 25; Custom of Chasam Sofer to not way Shema whil wearing Rabbeinu Tam Tefillin, recorded in Likkutei Chaver Ben Chaim, brought in Os Chaim Veshalom ibid; Minhagei Chasam Sofer 1/22 that he would not say Shnayim Mikra of Shema without Tefillin.
The reason: As the Biblical Mitzvah of wearing Tefillin applies throughout the entire day and hence whenever one reads Shema without Tefillin he is testifying falsely. [Os Chaim Veshalom ibid; Rebbe ibid]
 M”A 25/6 based on Sifri; Bach 38 in name of teacher Rav Feivish; Shlah, brought in M”A 25/6; Or Tzaddikim in name of Ramban and Rav Chaim Vital, brought in Shaareiy Teshuvah 38/3 “One is obligated to read all four Parshiyos”; Levush 58/2; See Levushei Mordechai 3/5 in name of Maharam Shick 23 that from the Poskim who write one is to recite Shema with Rabbeinu Tam [see footnotes below] it is implied that just like there is Eiduis Sheker to recite Shema without Tefillin, so too it is Eidus Sheker to wear Tefillin without saying Shema.