Are you using speaker phone? Are you using the Hand Set?

If you are using the speaker phone, the first thing is to check the back end configuration of your IP phone system and Make sure that that Station has the Microphone Feature enabled. If it does, then the next step would be to configure a different phone with your same extension and ip. If that phone works fine, then it tells you that it is the microphone inside the original phone that is bad.

If it doesn't fix it, then the problem lies on some of the settings within your phone system.

Some other simply things to try if using the Handset, is 1) Replace the cord from the telephone base to the handset. 2) Grab a similar headset and hook it up to your phone. Test calling someone internally in the office, and out of the office.