Date: 17 Tamuz 5564
From: Rabbi Moshe Sofer, Frankfurt am Main
To: Rabbi Pinchas Leib
The responsum addresses the requirement for tefillin straps to be processed 'lishma' (for the sake of the mitzvah), clarifying that the tanning process itself must be 'lishma' for the straps, unlike the batim (boxes), and discusses the permissibility of a non-Jew tanning many hides 'lishma' when only a few are intended for tefillin.
Source: Shu"t Chasam Sofer Collected §31