Drawing is one part.
Mechanics are the other one.
The physics engine deals with the mechanics (you have an object this shape in this position, how does it behave according to “physics” rules? those engine are the answer)
You have to deal with the drawings.
You can actually fuse them in one object that can be drawn and has specific parameter to be fed to the physics engine.
You should start with some tutorial or example
start from here
https://github.com/openfl/openfl-samples/tree/master/SimpleBox2D