May one put tefillin on while sitting or lying down if he is unable to stand, such as if he is sick, or bound to a wheelchair?

Answer:

Yes, one who is unable to stand is nonetheless required to put on tefillin in a sitting position. Thus, if one is sick, or wheelchair-bound, he is nonetheless to put on tefillin with a blessing while sitting. This includes both the hand and head tefillin.

Explanation: In general, unless explicitly taught otherwise by a specific mitzvah, all Mitzvos that require standing, are only initially required to be done while standing and if was done while sitting one nonetheless fulfill this obligation. The same would apply by blessings, that although initially one must stand for a blessing of the mitzvah, if one is unable to he may recite it while sitting. Furthermore, by tefillin we do not even find a Talmudic obligation to stand neither biblical nor rabbinical, and the entire idea of standing is unclear from the Poskim and is written in the Poskim in reference to the rulings of the Zohar regarding this matter, and is recorded as a custom of Jewry, and even then it is debated as to whether the requirement to stand is only by the head tefillin or also by the hand tefillin, as many are accustomed to sit when putting on the hand tefillin. If indeed there was a Talmudic obligation for the tefillin to be put on while standing, then it would not be possible to entertain that according to Kabbalah and many authorities the hand tefillin is to be placed while sitting, and therefore we can conclude that even the head tefillin which certainly initially needs to be put on while standing its standing obligation is not of the same level as that of other mitzvahs that require standing. The Tur and Shulchan Aruch doesn’t even discuss at all any obligation to stand while putting on the Tefillin, and its discussion is first brought in the Darkei Moshe and Rama based on works of Kabbalah, thus once again lending to its more Kabbalistic and traditional form of obligation versus an actual rabbinical requirement. Now while certainly in the end of the day due to the long-standing tradition of Jewry which is recorded in the Poskim one is required to stand when putting on tefillin, at the very least the head tefillin, there is no room whatsoever to negate the fulfillment of the mitzvah while sitting, and therefore one who cannot stand is put on tefillin while sitting as he would regularly do.

Sources: See regarding standing versus sitting when putting on the head and hand tefillin: Admur 25:27; Siddur Admur; Rama 25:11; Iggur in name of Zohar; Peri Eitz Chaim and Shaar Hakavanos; Matzas Shmurim p. 63; Kaf Hachaim 25:33; Rashal 98; Maryu 191 [brought in Kneses Hagedola 8; Machatzis Hashekel 25:20, Kaf Hachaim ibid]; Halacha Berurah Yosef 25:45