The phone displays that I have 3 missed calls, but in Voice Mail, I have no messages.

If you return to your office after being out, and you see a message "You have 3 missed calls" on the display, this is an indication that there were missed calls while you were out. You can review information about the calls by pressing the "Directories" button, selecting "Missed Calls" and using the arrow key under the middle of the display to scroll down (or up). If the callers left a message, your display would indicate "You have voicemail" and your handset light would be on. If there is no message indicator flashing then the callers did not leave any messages.