Adjusting volume on specific extensions

Is it possible somewhere in the FreePBX configuration to amplify or increase the volume going to a specific extension? We have an employee here who has a hard time hearing people when listening on the handset or the speaker phone of his phone, even though those two volumes are turned up all the way on the phone. Thank you for your help.

If the extension is analog, then you can make adjustments via the dahdi_* file. However, if it is VoIP, then you will likely need to make changes to the phone configuration files.