The Mishna on our daf introduces the idea that some mitzvot are obligatory only in the Land of Israel. According to the Mishna, with minor exceptions, those mitzvot that are dependent on the land – teluyot ba’aretz – only apply in Israel, while those that are not dependent on the land apply both in Israel and in the Diaspora.
The Gemara’s first suggestion of how to define the concept of mitzvot ha-teluyot ba’aretz is that it is based on whether or not the Torah discusses the mitzvot in the context of bi’ah – of coming into the land. This suggestion is rejected because of two mitzvot – the commandments of tefillin and peter hamor (redeeming a first-born donkey) – about which the Torah says ve-hayah ki yevi’aha, indicating that they become obligatory after God brings the Jewish people into the land of Israel (see Shemot 13:11), yet we know that these commandments apply in all places. The Gemara concludes that agricultural mitzvot apply only in Israel, while personal mitzvot apply in all places.
While the Gemara takes for granted that tefillin and peter hamor apply even in the Diaspora, it does not supply any proofs that this is the case. Rashi says simply that we know that Babylonian Talmud scholars wore tefillin, although Tosafot argue that this does not prove that there is a true obligation to wear tefillin in the Diaspora, since they may have done so on a rabbinic level. The Ramban at first echoes Rashi’s approach, but eventually concludes like the Talmud Yerushalmi that the mitzva of u-keshartam le’ot al yedkhem, commanding us to wear tefillin, appears immediately after the threat of exile (va-avadetem mehera me’al ha-aretz ha-tovah – see Devarim 11:18), implying that the mitzva of tefillin remains in effect even when the Jewish people are living in exile.