Everytime when i make a call in my iphone 5s the other person cant hear me but i can hear him clearly so when i quit the call and redialed to the same number everything goes fine. I bought the phone just 3 months back. How can i overcome it?

Restart your phone.

Try to reset your device. This won't delete your data stored on the phone.

• Press and hold the Sleep/Wake button
• Press and hold on the Home button
• Keep holding both buttons until the display turns off and back on with Apple logo on it.

Alternatively, you may go to Settings - General - Reset - Reset All Settings

https://support.apple.com/en-us/HT201559

If this does not help, restore your device to factory settings. Note that this will erase the data from your device.

Take a look this Apple Support article: Use iTunes to restore your iPhone, iPad, or iPod to factory settings - Apple Support.

If this does't help, contact Apple Support and ask for help.

https://www.apple.com/support/iphone/contact/

You are welcome. Hope these steps will help you!