Why would my microphone not work while making a call, but it works while filming videos or dictating a text message?

I have the iphone 5S. My microphone is not working properly lately. Specifically, when I try to use my phone to make a voice call I have to put it on speaker phone for anyone to hear me!?! Are there two different microphones on this model?? How do I fix it? It did get a little moisture on it the other day, but everything else is perfect but this issue?? Help! I can't live on speaker phone!!