Side note: a half an hour call on a commute train (or in public spaces) is considered extremely rude in many parts of the world.
It's rude to me as well. But I think we are wrong about this. I was in the doctor's office and a person was on the phone talking in the waiting room. I thought it was weird. But then I thought "if a person was sitting in the seat next to them and they were talking, would that be weird?" I don't think we'd see two people talking as being weird. Why is it weird if someone is by themself speaking to someone that isn't a…
Someone talking on the phone but facing away from the room isn’t usually considered rude, either.
In a waiting room or train car, if you’re sitting and talking on the phone or Zoom, you’re broadcasting into the room with your posture. Your voice tends to broadcast as well with no wall or other conversant as an immediate barrier.