the phalanx probably also has archeotech weapons since it was already in use before Dorn was even found by the emperor.So now as the Rock is basically a moon sized spaceship with weapons all around it, how would it fare against The Phalanx in a 1v1 duel ? No escort ships, no supporting fleet. Just these 2 fortresses against each other. Assault pods and small fighters launched from inside the fortresses still allowed though.
I think the Phalanx would destroy The Rock, but it'll be a very close fight. Phalanx was built for war, but The Rock is more of an improvisation of the remains of Caliban. Although the Archeotech weapons in The Rock might make a difference.