PhoneGap can build your app and package it in a format suitable to be uploaded to the Google or Apple app stores.
However the procedure to actually upload something to one of these stores is not that straightforward, you need at least a confirmed account and a signature with which to sign your apps (and additional steps). A google search points to http://www.androidauthority.com/publishing-first-app-play-store-need-know-383572/ and https://code.tutsplus.com/tutorials/how-to-submit-an-ios-app-to-the-app-store--mobile-16812
Hope this helps,
See also the documentation here: https://docs.mendix.com/howto/mobile/publishing-a-mendix-hybrid-mobile-app-in-mobile-app-stores