Reporting on the cell phone number in a Thon event will use the field titled Mobile Phone. 

Report on cell phone number for Thon participant:

1. Go to communities>special events>friends asking friends>Kintera Thon
2. Hover over the event name and go to report
3. Select the people participant detail report
4. Select a date range and click next
5. On the choose columns page select the field for mobile phone
6. Then select to finish and then run the report immediately