How is the lens attached to the phone?

Question

Video processing

I'm not a photographer, so sorry.
Bottom line:
1. I buy a phone case
2. I glue an adapter with a thread on it (for example, landcameras.com/accessories/new/filter-adapter
3. You can already attach filters to it, that's good.
4. If I want a lens ( for example, www.amazon.com/Rokinon-FE8M-C-F3-5-Fisheye-Canon/d... How
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Answer 1

What a mockery of the phone!
It is unlikely that you will be able to focus on the phone, because the lenses are designed specifically for specific lines of cameras and the distance from the mount to the camera's matrix is ​​strictly fixed...