Getting the private IP of the phone on my hotspot when it's connected to data

I want to use scrcpy remotely if I'm on mobile data, so I decided to turn on my mobile hotspot, connect to WiFi, and connect my laptop to it. Of course, that works. But if I disconnect from WiFi and connect to mobile data, there is no way for me to access my phone when I'm on the hotspot. Surely the phone would give itself a private IP on the hotspot, right? If so, how do I find it?