> It isn't like he is desecrating a temple, or intruding into your home and using your toilet, or jerking off in the public...

Just like jerking off, defecation should be done in private. Meetings are not private. Very few people want to see/hear/smell you do that and that includes over zoom or phone conference. Most people really do want to mind their own business, and that means having no part in you doing those very private things.

If someone is in a meeting on their phone while in a bathroom stall it's also very rude to everyone else in the bathroom trying to do their own business as privately as they possibly can under the circumstances.