The DataFormatString property for phone number will only works if your data type in that column is of
type like numeric. This approach does not work if you have
data type as string. Now the option is converting the data type of that column to something that can be formatted using the format string. You can try it in ItemDataBound event. Check out the following code snippet.
Thanks for your quick reply. I managed to get it format by below code. I am not sure whether this is a good solution. Do you have any idea performance wise which one will be better. Using a Template column or writing code in ItemDataBound.