RTW's phlanax formation was replaced by M2's Spear wall, it's hard coded and unchangeable.
Closest thing is to remove a pike units spear wall formation (note also you need to remove the long_pike/short_pike weapon attribute) and also remove thier secondary weapon.

If you do that, like RTW's phalanx they will take any non-pike head-on regardless of stats. Major downside is unlike the phalanx they have no particular weakness and effectively become an uber-unit without further tweaking, setting the attack delay to about 75 seems to be an effective balance for starters, though head-on even the weakest pike is still a little too powerfull.