Quote Originally Posted by konny
They will not hold the line against two other phalanxes, that's the point. It doesn't matter that they will hold out longer than any other Phalanx in the given situation before they break.
Did you even read what I said? They are meant to be used in the main battle line as any other phalanx unit, where they will usually not face more than one enemy unit except if the rest of the line collapses, not alone against too many opponents. They do exactly what other phalanx units but better and more reliably, but suffer from exactly the same fatal problem, namely vulnerability to flank attacks. Use them to either hold a strong central part of the line, or as an anchor on one or both of the flanks for cavalry to attack around.