Q: microphone not working while calling (phone

I've Iphone 5 16GB. I used to call on handsfree mode both on phone and viber. But now the while using handsfree mode the microphone didn't work. I've checked whether the microphone does have problem or not by using voice recording but it worked absolutely. I resetting the settings without erasing all datas but still not working. Can someone help me solve the problem?