Why won't my iPhone 4s play music without head phones but does with them?

I tried listening to pandora without headphones, on the speakers, and it wouldn't work there wasn't even a little volume adjuster. But it worked when I talked to Siri or do a speaker phone call.

Try resetting your phone. Hold the top and home button, the phone will reset. Let go of the buttons when the apple on the phone appears.

The speaker might be damaged, you might need to replace it