How to get PHone number to show on Call Back Screen

[breale]

How can I add the field phone number to the screen that shows up after I click on a CALL BACK activity. I can easily add fields to other areas of sugar, but for some reason, I can't figure out how to add it hear, and I don't understand why the phone number field doesn't show up by default for leads that you click into from the Activity or Calendar area.

Can anyone explain how to do this?