Volume keys are little-used but you will feel very inconvenient when they are broken.
Don't worry Virtual Volume Key can help you.

Virtual Volume Key can do the same things as physical keys and you can put it anywhere you want.
It will adjust call volume when you are in-call.
It will adjust media volume when you are listening to music or watching video.
It will adjust notification volume when the phone is in nomal status.

If your physical volume keys don't work or
if you don't want use physical volume keys for some reasons
welcome to use Virtual Volume Key.