RESOLVED. THIS ISSUE WAS RESOLVED IN AUGUST 2018 WITH THE INSTALLATION OF NEW PHONE SERVER.
Issue: When speaking to people outside the building, phone calls sound muffled, almost as if they were under water.
This issue occurs when the person you are calling or that is calling you is on the Sprint Network. There is no reason for this interference and it has existed for the last two school years. All contact with Allworx (our phone service provider) has revealed they don't know what the issue is.
Workaround #1: To make sure the issue is the Sprint issue and not one with your phone, unplug the phone from the wall for ten seconds and plug back in. The phone will go through a restart and boot back up. From there, you can try the phone call again and see if there is improvement.
Workaround #2: A possible workaround would be to contact the person using Google hangouts, cell phone, or have the person contact you from a different line not on the Sprint Network.