When included within a cordova/phonegap build then the application will not stop any background audio that is playing. Any application sounds will play over the background audio.
No further action is necessary.
cordova plugin add cordova-allow-background-audio
OR
cordova plugin add https://github.com/davidfig/cordova-allow-background-audio.git
The code is based on the answer to this question: https://stackoverflow.com/questions/14122363/iphone-app-allow-background-music-to-continue-to-play?lq=1
The plugin was base https://github.com/AubreyHewes/cordova-background-audio, which does the opposite of this plugin: allows your audio to run in the background when not the app is not in focus.