A Good Phalanx Formation and Strategy

[Watchman]

Nitpick: it's tactic, not strategy. Tactics win battles, strategy wins wars. Different scale.

That said, the main GCS problem in vanilla is the lack of decent "flankers". The Heavy Peltasts and Greek Cavalry just don't quite cut it when the push comes to shove, especially against more formidable flankers like heavy cavalry or decent shock troops like Roman or barbarian heavy infantry. If possible use mercs. Thracians and Bastarnae are pretty good if you can get them, although you'll probably need to detail at least one phalanx per each flank to ward off cavalry. 'Course, if you can use the merc heavies to support your own somewhat lackluster cav in dealing with the enemy flankers and then turn both against the flanks of the enemy's main line pinned by your phalanxes once those have been disposed of...