Suppose the textbox on the subform that has the Call ID is called txtCallID and the label in the main form is called lblTitle, then put something like this on the subform's On Current event and txtCallID's After Update event.
Me.Parent.Form.lblTitle.Caption = "Record for Call ID No. " & Me.txtCallID
Note that autonumbers are usually not something you show users. Those are more for the computer to keep track of records.
Michigan Dept. of Environmental Quality
Air Quality Division