Heh could also be your router?

Can you explain more about the routing issues? Because I've also been thinking about how practically everyone has an old smartphone with a broken screen in a drawer somewhere, and whether we could encourage people to use that for self-hosting. If you leave it at home, always plugged in and on your own network, I don't know how it would be different than any other device running a server?

No good reason to do this, but I would imagine you could set up a site-to-site VPN with Wireguard (or hell, Tailscale) from your phone to a VPS, and have people hit the public server which routes back over your tunnel to your phone for access to the data.

I'm almost curious enough to try for myself.