How to test game on mobile without publishing it?
right click on the bug item and click start network preview.
then type the url in your phone and viola
As @Slash says yu can test your game by accessing from your phone to the ip that GDevelop gives you when you run in network preview.
If is for testing on Android phone device you can export to APK and then install the APK in your phone.
It works, thank you guys.