Linux has few defenses against the compromise of individual programs leading to the whole system being compromised. If you stick to basic tools (command line) that you can fully trust, it might be somewhat resistant to these types of attacks. The kernel might be reasonably secure but in typical setups, any RCE in any program is a complete compromise.

Things like QubesOS can help, but it's quite high-effort to use and isn't compatible with any phone I know of.

It would at least be diverse.

Linux is swiss cheese and your dumb phone is probably full of zero days which will happily mitm you.

If you care about security, you should try Qubes OS.