iPhone 4 Speakerphone does not work

I have been around what seems like the entire internet looking for reasons why the speakerphone on my iPhone does not work. I can take a call and the caller can hear me but the moment I put it on speakerphone they cannot hear me any longer.

I have tried the various resetting options, cleaned out the small noise cancellation hole near the headphone jack and still nothing.

Voice memos work as well. I believe speakerphone uses a small mic that is attached to the power cable within the iphone 4. Just looking for clarification if I am correct that changing the power sensor cable will likely remedy the speakerphone issue.

THANKS !!!!!