In Fuller's "The Generalship of Alexander the Great" you get the impression they are more like legionaires or heavier Peltasts than Phalangites. That seems to be his interpretation, but it is not a bad one IMO, Alexander and Phillip (who built the army with which his son conquered the world) were not stupid and would have seen the advantage of such troops to supplement the Phalangati, Peltasts and cavalry.