In my home office setup, i have my laptop, and my mobile phone, with Zoom app installed on each. I join the zoom session from laptop and turn on my microphone and loudspeaker. I then join the same zoom session from my phone and just turn on its camera (I do not use the sound on my phone, i only turn on the camera) . I use a shoebox or similar to orient my phone to point down at a piece of paper where I can write equations. The host can use Zoom's spotlight control to force everyone to see the camera shot from the phone at all times. How to spotlight: https://support.zoom.us/hc/en-us/articles/201362653-Spotlight-Video