With an Android phone, you have to suffer with separate sound levels for each application type: alarm, phone ring, applications or whatever else. When you increase the global level on the main screen, there is no guarantee that damed application will keep it.
The iOS follows this mistake. For unknown reason, an application may have either the same volume level you set on the main screen or completely different one. For a long time, I haven't noticed any regularity there and still don't have a clue.
It's easy to reproduce: here I decreased the volume level to its minimum value. Now I open YouTube and it starts playing at almost max. Why? Was it so difficult to get the global value I set just a second ago?
I wish my device was like a physical record player. There were a tape driver, CD driver or even USB system on it, but the volume level was single an none of subsystems could change it.