As you can see, the light goes in via the camera lens that will presumably be visible on the back of the phone, then gets refracted by the mirror element towards the secondary lens elements inside. Moving those inner elements up and down a bit will produce the desired telephoto, optical zoom effect.
In one of the patent descriptions, Apple tips that the user may be able to choose whether to employ this system, or use a standard wide-angle camera for their photographic or video capture needs. Does that ring any bells?
Apple is working on an extra camera-centric iPhone 7 Plus of sorts that will cost more than what the larger of the annual iPhone duo typically commands. In exchange, the iPhone 7 Pro, or whatever Apple decides to name it, will offer a dual-camera setup, like on the LG G5, or the Huawei P9, but it will also employ optical zoom for one of the cameras to set its shooting abilities further apart.
This is not some wild speculation, too, as we've seen this rumor be confirmed by none other than the most reputable Apple analyst already, plus the alleged dual camera unit already leaked out in the flesh.
We asked you not long ago if you think that Apple can pull off a dual camera setup and bring something new to the phone photography table, and a lot of our respondents took the stance that if Apple is involved, it will be one of a kind dual camera undertaking. Looking at the patent drawing on the right, they might be right, if this thing materializes as rumored.