

Surely the simplest approach is not to use a wifi ssid that you don’t trust. Yes, mobile broadband is slower and more expensive, but is also more under your control, it is however harder for your boss to monitor.
If I was an it manager I’d probably want to keep an eye on WiFi traffic, even on the open ssid, just to see what’s going on. I don’t trust free WiFi.
If you can’t use 4/5g, and can’t find a suitable firewall or VPN, can you set up a different user on your phone? - and be disciplined in is use.
Battery replacement is an issue, but is easily solved with good design. I don’t need the thinnest phone that’s difficult to hold, a few extra mm won’t affect my life negatively. I’d rather have something usable and maintainable.
My biggest gripe however is the built in obsolesce of software support life. Perfectly good electronics are rendered useless by the system not receiving software / security updates after a couple of years.