Originally Posted by matteus the inbred
Surprisingly the Wikipedia page on Byzantine battle tactics is quite extensive and references all the same primary sources. It's possible that al Qa'Qaa was even referring to a Byzantine infantry attack in wedge formation. Further cross references on the subject of phalanxes bring up references to the skoutatoi using it, or something very like it. That's good enough for me.
Some evidence from these references also suggests that Imperial Roman legionaries could and did use phalanx tactics in the eastern theatres of war, so I think it's likely a continuation or innovation of the tactic rather than an invention.
Presumably the Greek term remained the same, or they used the term for a wedge, whatever that might be (since their cataphracts also usually fought in wedge formation), as the Byzantine Empire was Hellenized in language terms by Heraclius.