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.
The other issue is phones would not typically have a public IP without ipv6. You are also unlikely to have a static (consistent) IP address.
I don’t think it’s a great idea to host a website on cellular data. If I had to serve something with a mobile device, I’d use USB networking, or a USB to Ethernet adapter.