Modern smartphone security relies on verified boot which cryptographically verifies various components in the boot process all the way to the kernel and beyond to make sure they have not been tampered with. This not only protects against physical attack vectors, but also remote as it can detect and prevent malicious modifications to the firmware and OS.

For example, this makes malware persistence much more difficult, as verified boot checks for integrity at every boot and reverses any unsigned changes.

Persistence on iOS and Android is very difficult. As an example, at least on iOS, threat actors have sometimes failed to achieve persistence, so they hijack the shutdown process and simply fake shutdown by animating the shutdown flow. The user thinks they've shut down the phone, but in reality the device was never shut down and never went through the verified boot process. However, since Steve Jobs decided iOS never needs a manual reboot, gaining persistence may not even be necessary, because people don't reboot their iPhones.