With Windows Phone 8.1, Microsoft done a great job. It added the separate volume controls. But why it didn't added the volume controls in settings (like Symbian for example). And the apps for volume don't work in 8.1, unfortunately. So, I added a new voice on Windows Phone UserVoice to add the volume controls directly in the settings. So, if the volume buttons broke, we will have any problem.
This is the link to the post: Volume Controls in settings – Feature Suggestions for Windows Phone
This is the link to the post: Volume Controls in settings – Feature Suggestions for Windows Phone