The reliquary contains the relics of other saints and, importantly, the arm of St. Philip the Apostle. The reliquary as we see it is the product of many hands, working at different times.

The object consists of two superimposed elements belonging to different eras: the base, in the form of a hexagonal box, and the upper cylinder. The hexagon is constructed with two floors, with the lower cornice bearing an inscription. Within each of the six sides, through crystal windows, we can see a relic, identified by a figured plate. Contained within the profiles of the upper level are six glass cabinets, now empty. 

Above the box is the cylindrical reliquary with the arm of St. Philip, surrounded by six semi-columns with arched buttresses and statuettes. The cylinder closes in a small dome structured by six ribs, with crests and dragons, and culminates in a base bearing a statuette depicting St. Philip. Inside the cylinder, the relic is supported by a silver mount bearing an inscription. On the front of the bone there is a plaque with the engraved image of the saint of Byzantine manufacture from the 12th century. The arm of St. Philip was donated to the Baptistery by Aymar the Monk, patriarch of Jerusalem and former cleric of the Baptistery of St. John; for this, in 1422-1425, Antonio del Vagliente created the upper part of the current reliquary. The lower part contains relics that were probably among those donated to the Baptistery in 1394 by the noblewoman Nicoletta Grioni. Scholars propose that the hexagonal box was made for these by Matteo di Lorenzo, toward the end of the 14th century.