Don't worry! Its not your phones problem... It just your handfrees fault and the issue can be solved by changing the handfrees. You can also check your mic by simply going to settings then search diagnostics and then test your mic...
Brother, in every wired headphone there are connecting points for power, speakers and mic. You mic point in the phone is not connecting with hands-free, might be got carbon on it. Try cleaning with cottonbud or something with care, it will be fine hopefully
