You can also overlay your iPhone/iPad screen on your camera feed. I literally set this up just yesterday after being frustrated with trying to hold up my iPhone to show something in a zoom. I know Zoom offers a way to share your iPhone screen (like a screenshare) but it can be flakey (the airplay version is more flakey) and sometimes I don't want to throw the whole meeting into chaos by starting a screenshare.

Now I can just fire up OBS, switch my camera in Zoom to the OBS virtual webcam (which shows my main webcam), then toggle on my iPhone source and drag it anywhere I want in the frame.