Are you using a Panoramic gateway/router? If not, have you tried contacting your work IT for support?
Right now I have the cox Nokia modem and a nighthawk router ? My work IT is totally stumped.
Sorry, I don't have any experience with Cox fiber. I wish it was available in my area. Just know the basics of fiber/PON. I assume there is no way to hook the Cisco phone directly to the Nokia modem(ONT)? Can you apply QoS(in your router settings)to the phone? What kind of latency does a speedtest show from Speedtest.net? When the test is done it should show idle, download and upload latency.
PS. Here are my results on FIOS fiber for comparison.
