Print all 3 parts (Dock1.stl, Dock2.stl, Platte.stl).
Glue Dock1.stl and Dock2.stl together.

Insert the connector into the long rectangle of Dock2.stl.

Insert the Platte.stl into the 2 rectangular holes in Dock2.stl.
By moving the Platte.stl more or less into Dock2.stl you can modify the angle of your phone. Take care, not to stress the connector of your phone...
Perhaps you have to glue them together too when the angle is correct.