From the desk of Boruch Menachem Rizel 

Why we don’t wear Tefilin on Chol Hamoed

 The basic issue is as follows. The Talmud (Eiruvin 96a) explains why we do not wear Tefillin on Shabbat and Yom Tov – the festivals. The Torah describes Tefillin as a “sign” (“oas”): “And it shall be a sign on your arm” (Exodus 13:16). It is a special symbol of the love between God and Israel. Now the Torah also calls Shabbat and the festivals a sign – see Exodus 31:13: “But you shall keep My Sabbaths for it is a sign between Me and you for your generations…” (This applies to Yom Tov too in which we may not perform most types of labor – see commentary of Ritva to that Gemara.) Thus, it is not appropriate to don the “sign” of Tefillin on Shabbat and Yom Tov because such times themselves testify to the bond between God and Israel.

What about Chol HaMo’ed – the intermediate days of Sukkot and Passover? Are they too a sign between God and Israel? The Zohar writes unequivocally that one should not wear Tefillin on Chol HaMo’ed (Zohar Chadash, Shir HaShirim 79b). This is also the conclusion of the Vilna Gaon (O.C. 31:4).

The Shulchan Aruch (Orach Chaim 31:2) paskins explicitly, that one is exempt from Tefillin on Chol HaMoed, because like Shabbos and Yom Tov, Chol HaMoed has an “ose” element to it. This view was first mentioned and then rejected by Tosafos in Menachos, where he pointed out that Chol HaMoed has an “ose” element (Succah on Succos and isur achillas chameitz on Pesach) but while Tosafos paskined that one is nevertheless chayav in Tefillin, the Shulchan Aruch paskined that one is patur for this very reason. Later, in hilchos Chol HaMoed, the Shulchan Aruch (Orach Chaim 545:3) paskined that one is permitted to write Tefillin on Chol HaMoed “liatzmo” which the Mishna Brurah explains as meaning even if one is not going to wear Tefillin on Chol HaMoed one may nevertheless write the Tefillin.

 

There are those (Rashba) who hold that since Chol HaMoed is an “os” because of the matzah (Succos because of the Sukkah) it is forbidden to wear Tefillin since one already has the “os” of the holiday. 

In Eretz Yisroel the accepted minhag is not to wear tefillin on Chol HaMoed. The Divrei Torah above is a compilation from the following websites in alphabetical order.

https://aish.com/tefillin-on-chol-hamoed/

https://www.halachipedia.com/index.php?title=Tefillin_on_Chol_HaMoed&oldid=33957

https://ohr.edu/holidays/pesach/laws_and_customs/3468https://www.sefaria.org.il/Eruvin.96a.7?lang=he