The best tactics that I learned for myself when playing (and winning) the Epirote campaign was to have 15 units of "Phalangitai Deuteroi", 4 units of Toxotai, and my General - in a full stack army, of course. You set the phalanxes in phalanx mode and "defend" and simply march a ridiculously long line of troops around and place them in front of the enemy. Let them come to your wall of death. Stretch out your Toxotai the entire length of your infantry and make sure that fire arrows are on. Keep your general in the rear so he can run up and down the line blowing his horn as needed.

As far as flanks go.......you don't need to worry if your infantry line is longer than that of the enemy. If it isn't, or they're going to be buggers and use cavalry, then just face 1 unit on each end to the flanks. They can run and chase the cavalry if they have to, and your Toxotai can pummel them from their unprotected flanks/rear if they really become a problem.

Basically, if you have enough phalanxes, you should never lose.