This is one of two nearly identical bronze phylacteries from France, this one being from modern Avignon. The purpose, as made clear by the text, was to protect against harmful elements:
Thosouderkyo vinyard oumixonthei, divert from this property all hail and all snow, and whatever might injure the land. The god, Oamoutha, orders it, and you Abrasax, assist! Iae Iao. (Trans. R. Kotansky (1994), 47.)
Source: R. Kotansky (1994), no. 11 and Plate III.