I clarified with my Erloi neighbor the conduct in the Erloi Beis Medrash. In Erloi in Beitar tefillin are only put on at home before davening and not in shul at all. In Yerusholaim, the Rebbe has always worn tefillin in the Ezras Nashim or Sukka with a minyan of just 10 men accompanying him. In recent years a number of bochurim have jumped at the opportunity to daven with their Rebbe in a small group and joined bringing the numbers a little higher. However the Rebbe considers himself to be wearing tefillin in private and tefillin are never worn in the Beis Medrash by anyone.
Despite the words of Teshuvos Divrei Chaim, Tzanzer bochurim do NOT wear tefillin in EY. The Divrei Yatziv writed that minhag EY trumps even a teshuva from the Divrei Chaim and their long-standing minhag.