A few years ago a company called beast grip made a cage/case for the iPhones that would let you mount dslr lenses to the phones. I believe the mounts included were for Canon EF. Maybe there was a Nikon AF variant as well.

A friendly note: you mention it uses Leica M mount glass early on and end up saying it uses Leica L mount at the end. Those are two totally different mounts. I assume it’s one or the other, not both.

This seems to be a good concept idea. In practical use Leica M mount glass would be many times more expensive than the phone itself. Leica L mount glass, while still expensive, would be more practical and have the opportunity for autofocus integration. Additionally L-mount would open up the usage of LUMIX and Sigma lenses too.