One of the things about mobile phone is that there's 2 OSes on the phone: one that handles the phone stuff and the other that you as a user actually interact with. What's really scary about it is that the OS we do not think about is often licensed to the manufacturer (Apple, Samsung, etc.), closed-source, and dated. There's a lot of security firms that sell fake cell towers to law enforcement and governments and that gives them access to all of the data you send over the network. In older formats like 2G there was no encryption on anything sent over the wire.

If you dig into the fake cell tower rabbit hole you'll find what you're talking about to be an even worse problem.