What don’t you just create a WiFi with your notebook and use this WiFi from your phone? Or, the other way, create a WiFi on your phone (tethering) and then connect with the notebook to this WiFi?
That is what I actually do already! I connect the phone with the hotspot of the notebook because that is much faster than the Wifi network. But the hotspot IP did not work, only the IP of the notebook in the Wifi network. Your answer prompted me to check this again. Probably it was a missing firewall rule. Now it works! I use the hotspot of the notebook because that IP and therefore the server address remains the same (192.168.137.1), the IP of the phone changes with every new connection to the hotspot.
So thank you very much for addressing this!
(How) can I add the “solved” tag to this thread?