IPhone voice recognition or microphone not working?

I have the iPhone 4s with Siri. When I try to use Siri or make a phone call, my voice can't be heard. This tells me that the microphone or speaker (not sure what to call it, I mean the hardware piece that hears what I'm saying) is not working. However, when the phone is on speaker phone during a phone call, whomever I'm talking to is able to hear me.
Is the speaker phone microphone separate from the normal microphone for Siri and phone calls on regular setting? Is there any way to fix this?

Added (1). Will resetting my phone delete pictures, music, contacts, etc?

My phone also can record sound when recording a video.

Try resetting your phone. Hold the home button and the lock button until it resets.