Yep we can try lots of things! What kind of sound are you tapping on as your test? A ringtone in sound settings, something in a game, etc?
- I would try Settings -> Sounds first and look at what the ringer volume is set at there. (Let me know if this is where you were trying before, I have a few specific fixes in mind for ringer volume issues.)
- Try opening a movie (you tube, music/video app, anything) and try adjusting the volume there while the movie is playing. Any different?
- You can also try Settings -> General -> Reset -> Reset All Settings (NOT content!) which will reset the basic settings on the phone. A little annoying but may help.