I have a phone that just started an endless loop of going blank, then showing its address and then going blank again. I also have a sys alarm 101 showing. I have tried switching out the phone but that has not helped. Could I have a port going bad on a card? Any helps is appreciated.

Replace line cord. Check the jack. Check the punch downs. Swap the phone with another one. Does the new good working one go bad?

Alarm 101 is station lock-out due to excessive data errors. It's most commonly caused by a bad phone, but you already replaced the phone.

As Cans said, it can be a bad cable or jack. It could also be a bad card. Unplug the cable from the card. It the card is bad, the error will occur. If not, plug it back in and troubleshoot back towards the jack, isolating at each point on the circuit.

Using a systematic approach, you should quickly find the problem.