On H/H, playing as the Ptolemaioi, I've routed a huge, 52-man, Seleucid family member's bodyguards with a single unit of pezhetairoi.

Using the default formation the mod gives you makes your phalanx ranks too thin, methinks. With a unit size of 120 for pezhetairoi, I set my men to 8 or more ranks deep, depending on my need for frontage. The general's bodyguard will inevitable push it's way through the front ranks, but if your phalanx is deep enough, he'll just be surrounded by more spearpoints. Too shallow, and he can push right through and disrupt the integrity of the phalanx.