When was the Minhag of touching Tefillin during “Poteach” in Ashreh Tehillim 145 appeared? Is it Minhag of Shulchan-Aruch era or Rashi?
Answer:
It does not appear to be an ancient custom, and I know it only by mention in taamei haminhagim.
The idea of the minhag is that one should touch one’s tefillin often (to remind oneself of them), and this is one of the places that it became customary to do so.
Best wishes.