Well, you could change the mount effect to horse +2 or something instead of adding frighten mount to the attributes. Granted this will not scare the horses but it will dispatch them quicker and cause a casualty induced rout quicker which would be similar to the frighten attribute. And it should stop the routing previous to engagement from the rear of the phalanx(insert 5th grade joke here). Personally, I think the phalanx units are slightly overpowered as it is but its your game. Adjust it how you will enjoy it most. My 2 cents.