Byron Krieger asked:
Who permitted the wearing of tefiln on Shabbos? When was it disallowed?
The Kollel replies:
It is derived from certain implications in the verses that wearing Tefilin on Shabbos is not a Mitzvah. It is true that a minority of opinions (Eruvin 96b) assert one fulfills a Mitzvah by wearing Tefilin on Shabbos, at no point in history do we find that Jews did wear Tefilin on Shabbos. The reason for that is either because they followed the majority opinion, or that even according to the latter opinions there is no obligation at all to wear Tefilin on Shabbos. Rather, they may be worn on Shabbos, as Rashi tells us in Eruvin 95b DH Zug Echad.
(See SHULCHAN ARUCH OC 31:1 for the details of this Halachah.)
Be well!