Maaseh Rav Siman 20
Can copy this into an AI, or connect the whole library to your assistant. For deeper learning, you can directly use the original seforim, sites, and apps.
תפילין כל מה שהם בגובה הראש משובח. והקשר צ"ל תחת שפוע הקדקוד:
Sefaria Community Translation
The higher tefillin are on the head, the more praiseworthy. And the knot needs to be below the base of the skull.