My phone's volume isn't working. I press the volume buttons but the screen only says "ringer" and doesn't show me the level. When I go into the volume settings I turn it all the way up and I still don't hear anything except the ringtones.

Great! That's your first step; now you need to restore the software. Follow the directions in the article I linked to.

Take it to an Apple store and see what they have to say. If it can be fixed through software reset/restore, they will be able to help you. And if it can't, they will know that also.

Search (both of you) the web for "iphone 4s no volume bar" and you will see that you are - by far - not the first to have this problem, and that the cause is generally mechanical and not software. Resetting is good general advice for some issues but this one is common on the 30-pin connector phones and the typical cause is known. The phone thinks it's docked due to a bad or clogged switch in the connector housing.

Did you drop your iPhone or submerged it?

You don't know how to follow the steps in the article I linked to? Come on now.

Did you restore yet?

From a backup or as a new device?

Restore as a new device (don't load your backup file) to test & see if the problem is still there.

You must go to settings, then press sound. Scroll down and make sure that it says that you can adjust your volume by pressing the volume buttons instead of the ringer being adjusted.

Hopefully they resolved this back in 2014 when this thread started.