Where did the Greek consonant cluster "ps" come from? I tried finding resources to track down this fun-sounding consonant cluster but came with no information. I was thinking about a voicing change and fusion in the Afro-asiatic consonants b and z (As in Arabic biz'r - toasted pumpkin seed) from a Phoenician loanword of something, but that is unlikely for me. If it wasn't Phoenician loanwords, then how did the consonants p and s form together in the languages evolution?
It's important to note that whilst Greek does spell /ps/ with a single letter, it does not represent a single phoneme, but a sequence of two.
In native vocabulary, Greek /ps/ continues the Proto-Indo-European sequence ps, bs, bʰs, kʷs, ɡʷs, and ɡʷʰs (the latter three only if not preceded by u or w). In most cases these occur across morpheme boundaries (in particular, masculine & feminine root nouns whose stem ends in a labial stop will all have a psi /ps/ in the nominative singular).
Most word-initial /ps/ in Greek appear to be from the Pre-Greek substrate though. The exact linguistic affiliation of this substrate is unknown, but an Afroasiatic affiliation is generally considered to be implausible. See Beekes for more information of Pre-Greek.
There may be some words with /ps/ in them in Greek that are borrowed from Afroasiatic sources, but these will be few in comparison to the other two sources.