Using the phone : Making calls : Setting the microphone sensitivity
Setting the microphone sensitivity
During a call: There are four settings for the microphone sensitivity. With these settings you get better acoustics in noisy or echoing environments.
*Press and hold the key   . . . set the microphone sensitivity with    Save . . . the change is immediately effective and also applies to subsequent calls
 
If you do not save the setting, it only applies for the current call.