Replace these fields with records in a related table--one record for each value selected. Then your report simply lists these selected values. It is possible to set this up and still have a check box formatted interface for selecting the values during the phone call.
Replace these fields with a single text field and a 50 item value list and a check box format. If you put a large sized edit box formatted copy of this field on your report layout, it will list only the selected values and can be set to slide up/resize enclosing part to adjust to the number of values actually selected. This option is easier to set up than 1, but less flexible when it comes to reporting--especially if you wan to see summary statistics broken down by the number of phone calls that have a given value selected.