formatting issue for cells

[Tonykiwi]

HI
I am working on an export to CSV file from a client database which included mobile phone numbers. The export occasionally shows the format as >>6.42103E+11<<

The cell format is 'general' and it is only a few of the cells which cause this. If I click on the number it reverts to the correct output but when I click elsewhere it goes back to the above format.



I have changed to text and it makes no difference.

can someone explain what is behind this please and how to fix it?

thanks