Phallic charms were a typical accessory for the ancient Roman. It was believed that wearing these pendants would help ward of the evil eye. The Romans believed that the reaction caused by seeing these charms, the emotion, laughter or embarrassment, would ward off any evil spirits. It is thought that the charms were worn to be pointing away from its wearer, to dispel any negative energy directed towards the wearer. These kinds of pendants were thought to be very common, that even babies and soldiers were said to have worn them.
For more information on phallic Roman art, please see our blog post: Apotropaic Art: Amulets and Phallic Pendants in Ancient Cultures