If you are looking for the phone/tablet browser app (not native mobile), then I think this may help you.
When you go to create a new project, you have sample applications to start with.
Also if you want to explore native mobile apps, then there are other examples too. And a lot of content available online on Mendix youtube channel, Mendix academy and demo apps for mobile.
Your responsive web apps work on phone if created correctly to adapt phone/tablet browser. In that case, you just add a phone profile in navigation.