See the Vilna Gaon’s view, who ruled like the Shulchan Arukh (and not like the Rema) that one should not put on tefillin on Hol HaMoed. This is already a topic among the medieval authorities (Rishonim) (Tosafot, the Rashba in his responsa, the Rosh, and others): whether Hol HaMoed is considered a festival day—having the status of a sign, a prohibition of labor, and other criteria—and if so, then tefillin should not be worn, just as was ruled in the Talmud regarding the Sabbath and Jewish holidays. There is not necessarily any need to reach for the Zohar or Hasidic customs for this. The custom in the Land of Israel follows the Vilna Gaon.
In the Diaspora, Ashkenazic communities followed the Rema where they did not adopt the Vilna Gaon’s custom, while there the Hasidim relied on the Zohar and ruled like the Shulchan Arukh.