The prayers recited on Ḥol Ha-mo’ed reflect its status as a mixture of kodesh and ḥol. At Shaḥarit, Minḥa, and Ma’ariv, we recite the weekday prayers, mentioning the festival only in Ya’aleh Ve-yavo during the Amida. One who forgets Ya’aleh Ve-yavo but realizes it before finishing the Amida returns to the beginning of Retzei, recites Ya’aleh Ve-yavo, and continues through the end of the Amida. However, if he does not realize his omission until he has finished the Amida (even if he has not yet taken the three steps backwards), he must repeat the Amida from the beginning so as to include Ya’aleh Ve-yavo (SA 490:2).
Hallel immediately follows the conclusion of the Shaḥarit Amida. On Ḥol Ha-mo’ed Sukkot we recite the entire Hallel, while on Ḥol Ha-mo’ed Pesaḥ we recite “half-Hallel,” as explained above (2:7).
The Sages ordained that relevant Torah portions be read on Ḥol Ha-mo’ed. On each day of Pesaḥ we read a section of the Torah that mentions the festival, while on each day of Sukkot we read about the festival offerings as detailed in Bamidbar. Four people are called up to the Torah. This number expresses the in-between status of Ḥol Ha-mo’ed: on a regular weekday three people are called up, on Ḥol Ha-mo’ed four, and on Yom Tov five (Megilla 21a).
Just as one prays Musaf on Yom Tov, so he prays it on Ḥol Ha-mo’ed, because Musaf is in lieu of the additional offerings of the festival, and in this respect Ḥol Ha-mo’ed and Yom Tov are the same.
On Shabbat of Ḥol Ha-mo’ed, the prayers of Ma’ariv, Shaḥarit, and Minḥa are identical to those of a regular Shabbat, with the addition of Ya’aleh Ve-yavo in the Amida. However, the Amida for Musaf is that of the festival, with insertions for Shabbat; we mention Shabbat before the festival, as the sanctity of Shabbat takes precedence over the sanctity of festivals. Thus the berakha concludes: “Who sanctifies Shabbat, Israel, and the seasons.”
The Rishonim disagree about whether tefilin should be worn on Ḥol Ha-mo’ed. As is well known, on Shabbat and festivals it is forbidden to put on tefilin, because tefilin are a sign of the connection between God and the Jewish people. Since Shabbat and Yom Tov are likewise considered signs (“otot”), putting on tefilin then is an affront to the status of these holy days. As for Ḥol Ha-mo’ed, some say that since some melakhot are permitted then, it is not considered a sign, and therefore a man must put on tefilin then (Rosh; Rema). Many practiced this way in most Ashkenazic communities. Others maintain though that since ḥametz is prohibited on Ḥol Ha-mo’ed Pesaḥ and sukka is mandatory on Ḥol Ha-mo’ed Sukkot, Ḥol Ha-mo’ed indeed functions as a sign of the connection between God and the Jews. Accordingly, in order to avoid belittling Ḥol Ha-mo’ed by implying that it is not a sign, one may not wear tefilin on Ḥol Ha-mo’ed (Rashba; SA 32:2). This was the practice in Sephardic communities and some Ashkenazic communities. Today, in the Diaspora each community should continue following its custom. However, in Eretz Yisrael, the widespread custom of all communities is to refrain from putting on tefilin on Ḥol Ha-mo’ed. Everyone who makes aliya must adopt this custom of Eretz Yisrael.