Can Ashkenazi Tefilin Be Worn By Sephardim?
The box of the Tefilin contains four parchments, each with a different portion from the Torah. There is a disagreement between the Rambam and the Rosh as to which portions need to be open and which need to be closed. In this context, open means that the beginning of the Torah portion is written at the right margin of the column, while closed means that the portion begins in the middle of the column. The Rambam asserts that the first three portions in the Tefilin need to be open and the last should be closed, while the Rosh says that all portions should be open. The Shulhan Aruch (O.H. 32:36) rules in accordance with the Rambam and says that if the fourth portion is not closed, the Tefilin are invalid.
The Taz (O.H. 32:26) seeks a compromise between the Rambam’s and the Rosh’s opinions by saying that the fourth Torah portion should begin in between the right margin and the center of the column. Rabbi Ben Zion Abba Shaul (Or Lezion, vol. II, ch. 3, § 7) writes that the Taz’s approach is rejected by the Shulhan Aruch and that the Sephardic community does not rely on the Taz. On the other hand, the Ashkenazic community does follow the Taz’s view and thus if a Sephardic person borrows Ashkenazic Tefilin, a blessing should not be recited over them. The Chabad community follows the opinion of Rabbi Shneur Zalman, who sided with the Rambam, and thus a Sephardic person could use Chabad Tefilin and recite a blessing. An Ashkenazic person who wishes to use Sephardic Tefilin may do so and recite a blessing since the Vilna Gaon also followed the Rambam’s view. Indeed, Rabbi Shlomo Zalman Auerbach was known to wear Tefilin according to the custom of the Vilna Gaon.
Summary: A Sephardic person may wear Ashkenazic Tefilin but should not recite a blessing. One may also wear Chabad Tefilin and one would recite a blessing.