I think using phalanx is alot of micromanage to put them into right positions and not moving them to much around when engaging the enemy army. This makes them as i feel vunerable and it feels like an out of date fighting style. Its very easy to defeat hellenic armies with phalanxes with versatile units like light cavalry and missle/skirmisher units.

I think for using a army with phalanxes successful it all depends how you use you rear units to force the enemy into the center getting smashed by the long phalanx pikes.