This may help you: https://world.mendix.com/display/refguide4/Mobile+Forms
You can create mobile forms and use the same back end processes you currently have. To style the mobile applications you just need to create a index-mobile.html html page and put it into your theme package. Just go to http://localhost:8080/index-mobile.html then copy the source code into your theme package. You can then change the css src address and create your own css stylesheet which you can use to style the mobile application. I hope this helps!