When did Jews start the prayer practice of wearing Tefillin?
Teffilin is mentioned in four places in the Torah. The Jews started observing this practice in the desert. There is a tradition that the Patriarchs and Matriarchs observed the laws of the Torah on a voluntary basis even before the commandments were given. It follows that they were already wearing Teffilin in the time of Abraham, Isaac, and Jacob. But the generations in between probably did not wear them until the command was given.
Rabbi Mordechai Rhine
Cherry Hill, New Jersey