(Gr. phulakteria; i.e., "defences" or "protections"), called by modern Jews tephillin (i.e., "prayers") are mentioned only in Matthew 23:5. They consisted of strips of parchment on which were inscribed these four texts:
Deuteronomy 6:4-9; Deuteronomy 11:18-21, and which were enclosed in a square leather case, on one side of which was inscribed the Hebrew letter shin, to which the rabbis attached some significance. This case was fastened by certain straps to the forehead just between the eyes. The "making broad the phylacteries" refers to the enlarging of the case so as to make it conspicuous. (See FRONTLETS .)
Another form of the phylactery consisted of two rolls of parchment, on which the same texts were written, enclosed in a case of black calfskin. This was worn on the left arm near the elbow, to which it was bound by a thong. It was called the "Tephillah on the arm."
These dictionary topics are from M.G. Easton M.A., D.D., Illustrated Bible Dictionary, Third Edition, published by Thomas Nelson, 1897. Public Domain, copy freely.
Easton, Matthew George. "Entry for 'Phylacteries'". "Easton's Bible Dictionary".