Hi Howard,
Not totally sure what you are looking for, are you developing a mobile app and want to test/check how it looks on your mobile device?
If so you can check out the dedicated section on this in the Mendix documentation: https://docs.mendix.com/howto/mobile/getting-started-with-native-mobile#3-3-viewing-your-app-on-your-testing-device
If not please provide some additional details so we can help.
Good luck!
What kind of device do you mean?