Sounds like maybe a variant of Linear B? But I didn’t get the Massey’s part about the numbers, that made no sense.
The Phaistos Disk was made using “moveable type”, basically, the disk was mass-produced after a fashion, using carved dies or stamps, which were impressed into the clay when wet. The clay was then fired. I find the Barry Fell translation compelling (FWIW). Anyway, Linear B was a syllabary used to write Greek; it was derived or adapted from Linear A, which was apparently used to write some other tongue (something other than Greek; I find Barry Fell’s translation of Linear A to be compelling, FWIW).
The argument that the Phaistos Disk is a fake stems from a few different things: as an artifact, it appears to be unique; the use of dies to make it suggests nothing much, but can be interpreted as evidence of fakery; it was baked in an oven, rather than the fire which burned the Palaces to the ground during some unrecorded war; the script has never been found anywhere else, although versions of most of the characters have been identified in Linear A, Linear B, the Cypriote syllabary, and various undeciphered (mostly short) inscriptions in Anatolia.
The dies used to make the inscription have never been found, but if they were, it would mitigate in favor of authenticity, obviously. If authentic, it’s reasonable to guess that a number of similar disks were manufactured (otherwise, why dies?) and it seems as though they’d have shown up in other sites, particularly in Crete.