Well, phalangites wore linen cuirasses, bronze helmets and greaves, and carried shields. They were packed in tight ranks, so that they were protected not only by their personal equipment but also by the shields of the men next to them, the bodies of their comrades and that forrest of pikes. As javelin isn't the most accurate weapon you can find, it would be hard to hit those vulnerable parts from a sensible distance, so we shouldn't be suprised if Akontistai can't kill too many of them from the front.