Because the UPnP port is open.

Solution: First connect the phone to WiFi, then open the settings of the phone, find the wireless network WLAN and click to enter. Then change the IP settings to static and copy the number after the router options. Then open the browser, copy the number you just copied into the browser's address bar, enter the router's management background, and click on Forwarding Rules - UPnP Settings. Finally, turn off the status in UPnP settings.