It was added last year in iOS 16. It’s called Continuity Camera.

It’s a nice feature. The cameras on any iPhone are WAY better than those built into a Mac.

I’m sure that holds for Android/PC.

There's already a number of apps in the iOS and android ecosystems that allow this - as far as I can tell this is moving that to default in the OS rather than a third party app.

Yes. If you have an iPhone and a Mac it will just show up as a webcam device automatically.

I have found it quite useful when joining a zoom call with a group of people in a breakout room. Prop up your phone somewhere and it works like a conference room camera.

IIRC, you can only use an iOS device as a webcam for a mac.