This is likely due to some aspect of the app that requires a feature that is not compatible with phone devices. The Google store has a complex set of algorithms it uses to determine onto which devices the app can be installed. These parameters are not determined by the XDK, but usually are the result of device feature requirements associated with plugins that were included with your project.
Review the plugins and what they do. Also, your Google app dashboard may give some specific hints as to what is preventing phones from seeing your app. It could also be that some older phones cannot see your device because your app requires a minimum level of the Android API, which you set in the build settings.
