When I say “Constraint” I mean, inside of PHaT, there is a “Constraint” mode.
Check out the documentation, and look for “Editing physics Constraints”.
https://docs.unrealengine.com/latest/INT/Engine/Physics/PhAT/UserGuide/index.html
In Maya (I assume you are using Maya), just make sure all of your bones are connected to Root, and make sure your UP axis is set to Z.
I would suggest checking out some youtube videos, like this one and the video after that.
