There is no app in the app store, but you can run the site as a web app. This will create an icon on your phone, and it will look and feel just like a downloaded app.

For iPhone, you can add GPN to your home screen by going here:
https://www.globalpickleball.network?showAddToHomescreen=1

For Android, you should see a prompt automatically asking if you want to "add to home screen".