This will tell you how to use your iPhone as a webcam input source on your Mac (running OSX) for web based video conferencing apps such as WhereBy and VirtualEDH
So... How absurd is this setup? Well here in the opening of 2020 with the pandemic drying up the market for cheap webcams... it's a lot less absurd now than it would have been 3 months ago, and probably a lot more absurd after that whole thing clears up. Right now finding a webcam can be difficult.
Download a full screen camera app. I used FullScreeen which cost me one dollar in app to buy pro as an IAP