formatting a cell that already contains data

[dtbh54]

hi i hope someone can help.

I am trying to format some cells in a worksheet that
contains phone numbers. It was imported from an access
database minus the formatting for phone numbers.

I am trying to change the format but it is not working.

I select the a cell or group of cells and select format
cells. I select number, then special, then phone number
and click ok.

Nothing happens.

So i double click in each cell and hit enter and the
formatting changes. There are many numbers.

How can I change the formatting all at once.?

Thank you very much in advance.

DTBH