Hello there,
With the physics engine enabled, you need to think in terms op applying impulses/forces to the player Mesh (typically a box or cylinder impostor). Also the rotation property is skipped and instead the rotationQuaternion property of the Mesh is used.
There’s some details about this in the Learning Babylon.js book (Chapter 10):
Concerning controlling the player character with the Physics Engine.
And luckily also in the official docs:
https://doc.babylonjs.com/how_to/using_the_physics_engine
https://doc.babylonjs.com/how_to/forces
I hope this information helped you a bit further. Good luck! 
Q