How to make a proxy server from a mobile phone?

Question

proxy

The essence of the problem is this. There are three mobile phones with unlimited internet already connected. I want to bite off a piece of this Internet + use ip phones from my stationary server. Well, that is, the phone is not in the same local network with the server, it moves around the city and is always connected to the mobile network. The server is always connected via wired internet. You need to install some software on the mobile phone so that it can tell the server its ip, and the server is already accessing the Internet through the phone as if through a proxy. Is it possible?

Answer 1

Not only is the phone not on the same network as the server, but it (and possibly the server) is not on the public network at all.
Your phone is behind NAT and does not have a white address, you will not be able to connect to it from the outside, because nat does not work in the opposite direction, and the provider will not forward ports to you.
The only way to get the server to see the phone is through tunnels like a VPN or a client-server application with an external server where the phone and your server can connect. Something like this.

Answer 2

raise the VPN (server on the phone). naturally, only outgoing connections will be available, because you do not have a permanent external IP. but isn't it easier to take a 3-4G modem? especially since the speed drops as you move.