שולחן ערוך אורח חיים · סימן מ״ד

English

One may not even nap while wearing his shel rosh and shel yad. If he covers them with a kerchief and he is not with his wife he is permitted to nap. This means he should rest his head between his knees and he may nap while sitting in that position. If one binds his tefillin to his hand he may even sleep but if they are not bound to his hands he may not even nap. Rama: This restriction applies when he is holding them outside of their case but if they are in their case it is permitted.