Any instant web form deployed in the Wolfram Cloud can be used as a mobile app from within the Wolfram Cloud app. Use IconRules to specify app icons for particular mobile platforms.
How to: Create an Instant Web Form describes creating and deploying instant web forms.
To set up a custom icon, use IconRules, giving any expression or image as an icon to use:
Some input types are treated specially when they appear in an instant form within a mobile app. For example, "Image" typically gives access to the camera and photo gallery on a mobile device.