Howdy pluton2128,
It sounds like you are using the phone in speaker phone mode but it doesn't seem to be picking up your voice. I would start by troubleshooting the software and quitting all the running apps on the phone:
Force an app to close in iOS
1. Press the Home button two times quickly. You'll see small previews of your recently used apps.
2. Swipe left to find the app you want to close.
3. Swipe up on the app's preview to close it.
When you have done that restart the device and test the issue again:
iOS: Turning off and on (restarting) and resetting
If the issue persists, backup your device to iTunes, then restore it as new and verify that it works.
How to erase your iOS device and then set it up as a new device or restore it from backups
If it does, then restore your backup to either verify it still works and the software just needed reinstalled, or isolate the issue to the backup file itself.
If none of that works, then you will likely need to have the phone serviced:
iPhone Repair and Service
Thank you for using Apple Support Communities.
Thank you for using Apple Support Communities.