Hand holding the phone makes for wobbly video and a phone on a desk is too low to give a good angle. A tripod with clamp holds the phone securely at a good height. It is still possible to pick up the whole unit, if necessary, and move it to another location.
When WebEx started, it offered to call me for the sound, so I accepted this option. One bonus of this is that if you receive a phone call, the conference audio is put on hold, so there is no risk of the conference participants listening in on my phone call.