Back in 2009, anynone with a Nokia could have a personal website running on their own phone. Sadly this amazing piece of tech was never widely adopted. Today’s phone are far more powerful than those Nokias both in performance and battery backup and still we don’t see anyone running a server on their phone. Why?
I think this was never implemented on phones because there’s no incentive for large corporations to work on something like this.
I think a root app that runs on Android 4 would work but the devs would have to implement modern standards (TLS 1.2) themselves, the performance would be bad and the phone will probably have known security vulnerabilities.