Breslover Chassidim follow the view of the ARI zal and Baal Shem Tov, based on the Zohar and many Rishonim, not to wear Tefillin on Chol ha-Mo’ed. Reb Noson expounds upon this in Likkutei Halakhos.
(Re. the Baal Shem Tov, see Imrei Pinchos 751; Shivchei Baal Shem Tov 6; Shulchan ha-Tahor [Komarno], Hilchos Tefillin 31:1. Re. the Zohar, see Zohar Chadash, Shir ha-Shirim, 64b; also note Rabbi Chaim Vital, Sha’ar ha-Kavannos, Drushei Chazoras ha-’Amidah, Drush 2, 38b. Rishonim who take this position include: Tosefos on Menachos 36b; Teshuvos ha-Rashba and Ra’avad, as cited in Shulchan Arukh, Orach Chaim 31:2. Cf. Likkutei Halakhos, Tefillin 6:4; ibid. Chol ha-Moed 1:3.)