I would suggest using Tailscale. It’s an app that runs on your local and remote computers. You log in with your google account, get a special up address that starts with 100.x.x.x. Then you use the special IP address to connect through ssh or mount a volume through samba.

Yes. It’s a default option for Tailscale. You just need to run the Tailscale client on the server with the exit node option, enable it in the web portal, and then tell your phone to use the exit node.