1) In a very limited way, there may be an exemption from the mitzvah of tefillin for a person who is completely consumed by his continuous involvement in another mitzvah.
2) Likewise, if a person is mentally/emotionally distraught or in physical pain to the point that he would not be able to think about his tefillin, he may qualify for an exemption as well, in limited cases.
3) When one dons or removes his tefillin, he should be careful not to uncover his head in front of an open Sefer Torah, or before his ‘rebbe muvhak’ (primary Torah teacher).
4) If a person has limited funds, he should sooner buy mezuzos for his home than a pair of tefillin. The reason is that he can borrow tefillin daily; he can’t borrow mezuzos!
5) One who was excommunicated by the community – according to the ancient laws of the ‘nidui’ halachic excommunication) is not permitted to wear tefillin!