just check out the help for a start. XRefs are very simple really they are like instances except instead of referencing (and copying) an object inside your current scene, xrefs reference a model (or scene) that was saved earlier to a .c4d file. An object in a scene can also be converted to an xref (which saves it to a file as well) but if it was animated the animation gets saved in the xref. In your case I would save all your phones (just the phone objects) to their own files (make sure they are all at the spot in space in each of the scenes). Use one of them as a xref in your scene, animate it, once done you can then just change the link inside the xref and a different phone object will be referenced but will use the same animation. That’s why it’s important to make sure they are lined up the same first.