Sefer Ha’mitzvos Ha’Katzar (the concise book of mitzvos)
By the Chofetz Chaim
This book lists the Torah mitzvos that can be observed today
First Section – the Positive Commandments
8. It is a positive commandment to tie tefillin on your arm
As is says in Devarim (Deuteronomy) 6:8, “And you shall tie it as a sign on your arm.” And the place to put them is on the biceps, at the raised part.