It kinda seems like it would be difficult and not really do any damage. Also, how would you go about attacking a phalanx?
Hoplite or pike phalanx?
I'm not an expert or anything like that. But I would think that the deeper phalanx (more men pushing the front line) would be able to push the more shallow phalanx back little by little. I would also think that you would have another unit trying to flank the enemy phalanx.