I've had similar issues with a single phone on my network.
There are 6 phones that work perfectly, but the most used one winds up with slowed down, choppy audio at least once per day. Rebooting fixes the immediate problem, but the issue comes back.
I've replaced the phone (an Obi1062 over wired (pass through, then tried wifi, then replaced it with an Obi1022 on ethernet (pass through to pc), then added an ObiWiFi to the Obi1022 and tried running it over WiFi, today I put a switch in and am trying it over ethernet, but without the pass through - hopefully this configuration works)
does this seem related / any advice?