Early Christian tradition states that Philip, along with his daughters, settled at Hierapolis. It is probable that Philip the Apostle (= disciple of Jesus) is the actual person, although a confused tradition suggests that it was Philip the Evangelist (see activities in the book of Acts.).
Tradition states that Philip was martyred and buried here at Hierapolis. On a hill northeast of the city a Martyrium—a memorial that was a focus of pilgrimage—was built in the fifth century AD. The outer walls of this structure form a square and inside of them is an octagonal memorial.
Prior to 2011 it was thought that the Octagonal Church (Martyrium) marked the spot of the burial of Philip, but it was discovered that the actual Church/Tomb was located on a hill 120 ft. [40 m.] from the Martyrium. For an article announcing the discovery, see here.
For a recent description of the Martyrium of Philip and a discussion of which Philip is being referred to see D'Andria, Francesco. “Conversion, Crucifixion and Celebration.”Biblical Archaeology Review vol. 37, no. 4 (2011): 34–46, 70 and more briefly Mark Wilson, Biblical Turkey — A Guide to the Jewish and Christian Sites of Asia Minor. Istanbul: Yayinlari, 2010, pp. 243–45.