Can't VNC from phone to tethered computer

Scenario:

Computer tethered to iPhone via Wifi, VNC server running on computer. VNC viewer (in this case iTeleport) running on phone. This is a carputer that uses my phone for internet connectivity and runs plex media server to send audio / video to connected clients. The clients connect to the computer via a mini wifi router (no internet connectivity), and the computer is set up to automatically connect to the tether connection SSID of my phone.

I would like to be able to control the computer via the iPhone via VNC. I can connect the computer to the phone via wifi, but the VNC viewer on the phone can't see the VNC server on the computer.

Assume that tethering is employing some form of AP Isolation (or similar). Wondering if there's a way around that. I can connect the phone to the mini wifi router, but then the computer loses internet connectivity.

The tethered computer (for completeness, not that it should matter) is running Win 7.