I tried going this route a few weeks ago. There's a few pretty big problems with current phone-based solutions:

- You need to fiddle with your phone (which is probably mounted to a monitor?) any time you want to turn on your webcam

- There's a perceptible lag on the final video, not ideal

- Phone needs an external power source, charging-over-USB usually isn't enough to power a phone with an always-on camera

- The phone will get hot, as it's not designed to run camera constantly

- For Android, your best option is to stream video over USB, which means enabling ADB and developer settings, which is inherently insecure. It also makes the charging problem above trickier, as phones usually only have the one port.

Honestly the best phone-based solution right now is to join the meeting twice - once on your personal phone for sending video, and once on your computer for sending/receiving audio/screenshares.

It probably would, and there are apps to do exactly this. Mounts are cheap enough to be reasonable, though there aren't many specialized for this yet.

Personally I don't think they'll even take half of this market - it means you can't fiddle with your phone while on a call.