When you remove a spec point from Dread Phalanx in the Summon Skeleton skill, it does not remove any already spawned skeletons. For instance, if I have two skeletons summoned and one point in Dread Phalanx, they are the larger version of the summons.
I can then remove a point from the skill, raising the maximum number of skeletons that can be summoned, and summon two more normal sized skeletons. This gives me two large and two normal size.
This is probably not a desired behavior. I would imagine that if you have minions summoned and change the skill associated with them, like removing something that effects the maximum number summoned, it should probably remove ones that you no longer have the skill points for.