Port forwarding for UDP 53 not working

My Ooma Telo Air VoIP phone requires port UDP 53 open (among other ports). I have configured such under network settings / port forwarding, but the port continues to be blocked when I run diagnostics on the Telo. I know I have entered everything correctly, as all the other 9 port forwarding entries work. Only UDP 53 remains blocked. I have checked the device IP address and it is correct. I have tried deleting and re-entering all entries and the same problem persists. Is there something unique about port 53 on eero?