The phone is the last but one "urgency" level. It means that if someone calls me on the phone it is really urgent. I would interrupt a lot of things, including

The phone is the last but one "urgency" level. It means that if someone calls me on the phone it is really urgent. I would interrupt a lot of things, including a presentation, if I get a call. If this is to say something minor I will block that person, or never pick up their call again.