The claim that Latin P and Greek Ph represent different phonological sounds is a matter of linguistic fact and common knowledge, as Latin /p/ is a voiceless bilabial plosive while Greek /pʰ/ historically represents an aspirated voiceless bilabial stop.
The claim states a basic linguistic difference between Latin and Greek phonology (plain bilabial stop vs. aspirated bilabial stop). This falls under common knowledge within linguistics and historical phonology, rendering specific citations from the provided retrieval set unnecessary, as none of the papers directly evaluate or compare the complete phonemic inventories of Latin P and Greek Ph as their primary empirical thesis.