Hi sue22306,
Thanks for visiting Apple Support Communities.
If you can't be heard on calls, try these troubleshooting steps first:
- Make sure nothing is plugged in to the jack connector.
- Make sure nothing is blocking any of the microphones (see the pictures below to locate the microphones on your device)
- Make sure none of the microphones is obstructed by dirt or debris.
- Turn the iPhone off and then on.
- Make sure that the latest version of iOS is installed.
- If necessary, find general iPhone hardware troubleshooting suggestions.
- For further assistance, contact Apple Support.
You can find these steps and more information here:
iPhone: Microphone issues
http://support.apple.com/kb/ts5183
Best Regards,
Jeremy