Question: When a person buys tefillin, the shel yad often comes with a cover within the cover, which many people leave on during davening. Is this proper?
Answer: The halacha is not clear-cut. The Rema (Orach Chayim 27:11) states that the Shulchan Aruch contends that it is preferable not to cover the shel rosh but the shel yad can be covered or uncovered. The Aruch HaShulchan (27: 22) presents this ruling as the accepted halacha.
The Mishnah Berurah, however, rules that it is better to cover the shel yad (Orach Chayim 27:47). The Sha’arei Teshuva (O.C. 27:11) cites the Levush, who provides a rationale for covering the shel yad. Devarim 6:8 states that tefillin should be “le’ot al yade’cha – a sign upon your arm.” Traditionally, this has been interpreted to mean that the shel yad should serve as a private sign – for you and not for others. Thus, it should be covered.
The Sha’arei Teshuva cites the Birkei Yosef who states in the name of his grandfather, Harav Azulai: “There are those who are scrupulous to cover their arm with their tallit when they don their tefillin and this is the proper procedure.”
Rav Yehuda Leib Tzirelson, chief rabbi of Bessarabia (Responsa Ma’archei Lev, Orach Chayim 1), ruled that one should remove the shel yad’s cover before making the berachah “leha’niach tefillin” so that one is making the berachah over the shel yad in its natural, pristine condition. It is a sign of kavod for the shel yad. After the berachah, he writes, one may cover the shel yad to protect its corners from becoming worn out if one wishes to do so.
So we have three opinions. All of them agree, however, that post facto, wearing the shel yad without a cover is okay. As such, a person can follow his father’s or rebbe’s custom without concern.
Some people nowadays seem to have the minhag of covering their shel yad with their shirt sleeve. They may perhaps be acting in accordance with the position of the Birkei Yosef who writes that a tallit can serve as a covering for the shel yad. (Technically, every modern-day garment can be referred to as a tallit.) Or they may be acting in accordance with Rav Tzirelson’s view that a covering for the shel yad is necessary (so that it serves as a private sign). The nature of this covering is irrelevant. A shirt sleeve works, as does the special shel yad box covering that usually comes with a purchase of tefillin.