The cliched notion is that the phalanx was this lumbering block that could only move forwards, barely able to do anything once set on its course.

While that's not quite true, I've seen assertions that one of the tactics was for the phalangites to charge by sprinting. I can believe a jog/double-time is possible to remain in formation, but I'm struggling a little to see how someone holding a very long pole with both hands (even a counter-weighted one) could sprint easily. Moreover that the phalanx would retain any cohesion with men running at different speeds, tripping over each other and so on.

There's also some stuff I was reading about how Philip's military reforms involved a lot of close order drills, changes of formation and the like to allow a much greater degree of flexibility.

So what was the deal?