A unit that has the Phalanx special ability...

It has long spears which are normally pointed up. Like this they can walk and run...

Hit the Phalanx ability and they lower their spears and get ready.. You can still move them at a walk (same spped as normal) but they can not run....

I have not really experimented but what seems to kill a unit in Phalanx mode is getting the formation mixed up and broken...