Volume

If you check Settings>Sounds & Haptics, do you have Change with Buttons turned on? If you do, when you are on the main home screen with nothing open there, if you tap on the volume up button, you should see the volume indicator appear at the top of the page and show the line moving to the right each time to tap on it. That will show your ringer volume.

If you have Music open, while the music is playing, you can tap on the volume up button, and you should see the volume icon appear on the left side of the screen and rise as you tap. The only difference here is if you have the individual song screen showing up and you will see the volume slider under the music controls and that will show it rising as you tap the volume button.

Call volume can only be adjusted while you are in a phone call. While in the call tap on the volume up button and you should hear the volume rising in your ear.

If this is not happening for any of these things, then use the Get support button on the top of the page here and contact Apple Support for assistance. Alternatively, if you have an Apple Store close by you, contact them and make a Genius Bar appointment and have the Genius examine the device. They will explain your options. Genius Bar Reservation and Apple Support Options - Apple

There are at least 2 separate volume settings on the iPhone. What sound are you referring to, the ringer, alarm, notifications, earpiece sounds when in a call, speaker volume when listening to music or video? Please explain which one and what troubleshooting you have tried so no one asks you to do something you have already done.

You're welcome.