Phone in Definition 1 of 3Pro Tip 1/3Workplace Communication Used to inform about absence or illness without going personally. Mark wasn't feeling well, so he decided to phone in and take a sick day. Pro Tip 2/3No Excuse Needed Simply stating unavailability without giving a reason is often acceptable. I'm not up to it, I'll just phone in. Pro Tip 3/3Brief & to the Point The call is usually short; details are not necessary. Phone in, say you’re sick, and disconnect. That’s it.