My favorite tatic with phalanx is recruit some palanx units, say 2 or 3 and have the main army behind it with a wing on each end to stop flanking, the AI 7-10 phalanx trooops will
atttack your own engulfing thm, then send the hastati on the flanks, the heavy skirmishers and cavarly destroy the units gaurding the AI's flanks and the classdial hoplites charge the phalanx flanks in a very long and thin formation.
Trouble is as often as not I've discovered I've given them no-whre to run to and they fight like lions.