The Phrygian evidence divides into two bodies that answer different questions, and neither answers the ones a reader most wants asked.
The first is Phrygian itself. Old Phrygian inscriptions, written in an alphabet related to the Greek, are short, and they are mostly dedications and funerary formulae. New Phrygian, from the Roman period, consists largely of curse formulae protecting tombs. The language is Indo-European and is understood in outline, but the corpus is too small and too formulaic to yield narrative, and readings of individual words remain contested.
The second is Greek and Roman testimony, which is abundant and is about the exported cult rather than the Phrygian one. Writers describe the Magna Mater at Rome, her festival, her eunuch priests and the myth of Attis, and they do so from within a Mediterranean religious world in which the goddess had already been reinterpreted for several centuries. Using that material to reconstruct what was believed in Phrygia is an inference that has to be made carefully and is often not.
The monuments themselves are the third source and the most directly Phrygian: facades carved into rock in the highlands, with geometric patterning and niches holding the goddess, some of them very large. They establish where she was worshipped, at what scale and in what visual language. They do not speak.