The Vilna Gaon was known to have remained adorned in his tefillin for the entire day, and his talmidim wrote (Ma’aseh Rav, Hilchos Tzitzis and Tefillin 18) that his practice should be seen as a public ruling – one is permitted to spend the entire day adorned in his tefillin in this day and age, even while performing mundane actions or eating a snack. They need not be removed while speaking of mundane but not frivolous matters such as discussing the news or any other non-mitzvah related conversation.
The Biur Halachah (37:2) writes that one who can fulfill this mitzvah all day is praiseworthy, but only provided he is sure of his ability to exercise proper halachic-mandated caution, or at the very least refrain from laughter, frivolity, and physical uncleanliness. The Shevet HaLevi (9:18) warns not to encourage public full-day donning of tefillin because most people cannot meet the necessary requirements.
It seem this difference in opinion results from a machlokes achronim (Sha’agas Aryeh 37- 40; Mishnah Berurah 44:3) as to the kind of concentration required while donning tefillin – is it retaining full focus of carrying the King’s insignia, or only a prohibition from unnecessary speech and frivolous behavior? While the first kind of concentration is nearly impossible today beyond davening time when one is naturally involved in speaking to G-d, the latter form – while no simple endeavor – isn’t completely impossible.
