If that is Avaya Door phone it has to be connected to station port and programmed as "Door". Controller has to be hook up to Contact closure on the ACS and has to be programmed accordingly. If this is Viking Door phone then it has to be connected to the Line port and that line has to be programmed to ring. So, press Feature button, dial 00 and press "Door" button to make sure it shows Line4 and its Green color.