Your phone keeps track of all missed calls and displays them in a few different ways. Understanding what each light or icon means can help you keep track of what you've missed.
On the IP35 desk phone (most common), the light on the "Messages" button will light up any time you've missed a call. This happens regardless of whether or not you've received a message. If you're using the IP55 desk phone the "Call Log" button will light up.
The light located at the top of the phone functions the same for both models: It lights up when you have a message waiting. (Note: The light will also flash when you receive a call.)
Please see the following link to the DAS Unify instructional PDF document:
https://www.oregon.gov/das/OSCIO/Documents/Understand-the-missed-call-lights.pdf
Please see the following link to the DAS Unify instructional video: