The Mishna Berura 31:3 explains why we do not wear Tefillin on Y"T as follows;
ויו"ט ג"כ מיקרי אות דבפסח מצרים כתיב אות והוקשו כל מועדי ה' בפ' אמור
The Rishonim all give different reasons for it, whether it is because Y"T is also called Shabbos, or because it is assur to do work, none of them (that I found) give this reason.
The Shaare Tzion brings the source as "Achronim". I checked over 10 Achronim who all give the other reasons, none bring this reason.
So my question is as folows;
- Which Achronim is The MB referring to?
- Why did he need a different reason than all the Rishonim (Tosfos, The Rosh, etc.)?
- Which Passuk is he referring to when he says that Pesach is called a "ois"?