Hardly. You put your phone on the desk and it's going to show the ceiling. In contrast to this, people do all kinds of weird things in front of laptops. I've even heard once of someone who allegedly masturbated (!) in front of a laptop. Of course, that must have been an extreme outlier ...

Remote code execution on a cell phone is thousands of times harder than a PC. If you have a RCE for the newest iOS software then there's people who are ready to pay you millions.

An up-to-date Nexus or iPhone is about the most secure thing you own.

Yes. They should have a switch.

This should definitely be a concern, but I feel like most people don't even realize that anything like that could happen. There is lots a news about webcams, baby monitors, etc. being hacked, but barely any warnings about making sure you keep your phone protected and secure, too.