Matthew 23:5

But all their works they do to be seen of men: for they make broad their phylacteries, and enlarge the borders of their garments ...

John A. Broadus, quoting Rabbinical writers, described the phylactery as follows:

In Exodus 13:16; Deuteronomy 6:8 and Deuteronomy 11:18, it was said to Israel concerning the teachings of the law, that they should be bound, "for a token upon thy head, and for frontlets between thine eyes." In the inter-biblical period, we find the Jews converting this figure into outward fact. They took four passages adjacent to the thrice repeated injunction, namely, Exodus 13:2-10; Exodus 13:11-17; Deuteronomy 6:4-9; and Deuteronomy 11:13-22, and writing them on strips of parchment, encased the folded strips in minute leather boxes. These four boxes were set on edge and fastened upon one leather base, which was placed in the middle of the forehead, and held there by a string tied round the head with peculiar knots which had a mystical meaning.[1]

Naturally, the bigger the phylactery the more attention the device would get for its wearer. If this seems strange to anyone today, it ought to be remembered that the making of a figurative statement to become a literal statement is an error that certainly was not confined to ancient Jews. The doctrine of transubstantiation is a similar error, resulting from exactly the same kind of mistake, and just as illogical.

Borders of the garments were considered sacred by the Jews, and the enlargement of the border was another device for ostentation and gratification of the pride of its wearer.