I had a discussion with Wien1938 about Pergamon's army yesterday, and apparently they didn't use phalanxes much. Here's what was said:
Wien: Pergamon does not appear to have phalangites (pikemen). I explained this to Quinn a long time ago. Phalangites must be kept in regular training so require a great deal of organisation and resources (i.e. a powerful kingdom) to create and maintain.
Pergamon seems to have had a core of xystophoroi, javelin skirmishing cavalry and call on the citizen foot of Pergamon itself (who were not very good)
Otherwise, they were very rich and hired lots of mercenaries.
Wien: Bactria is a mix of Macedonian colonists (xystophoroi, phalangites), Persians (xystophoroi), Bactrian cavalry (light but skilled javelin horse), Saka (horse archers), mountain Indians (light spearmen and longbow archers), some Cretan settlers and some Psidians who provided a core of theurophoroi type peltasts.
I say:
And cataphracts?
Wien says:
After 151 BC in Bactria, while after Antiochos III was defeated by Rome, Pergamon took over some of the old provinces and gained access to phalangites and Seleucid cavalry and cataphracts from the military colonies.
I say:
So should we make Pergamon be able to recruit any phalangites? If so, when?
Wien says:
The answer is no. Pergamon had no access to those troops until she gained the military colonies.
I'm not sure how you'd arrange it to allow them to train them. Unless we list them at the highest military development...
(...)
I say:
What about the EB units: Eastern Axemen (not spearmen), archers and peltasts, Hyrcanian Hillmen (axe units as well), Median Cavalry, Babylonian Spearmen, Arachosian skirmisher cavalry, Bactrian cavalry, Parthian horse archers, and perhaps a few more that I don't recall from my Bactrian campaign
Wien says:
All valid as far as I recall.
I say:
Well, the East can do with a few more units. Oh yes, I forgot the Caucasian spearmen and archers. I have heard something about (Caucasian) Iberian lancers. Have you heard of them?
Wien says:
Probably based on Rhoxolani cavalry. Scale, long lances (later the kontos), bow.
Spearmen are fairly ubiquitous and archers likewise.
A point worth mentioning is that the Hellenistic way of war tended to use archers and slingers as skirmishers, much like javelin skirmishers but supporting each other.
Wien says:
The Hellenistic theorists tend to lump all such troops as Psiloi.
Based on that, I'd say Pergamon would be quite an interesting faction to make and play as.