[AccessD] Phone Number with optional extension

Dear List:
 
I need to print a phone number in a report that has an optional extension of
up to five characters and can't seem to get the right mask.  I'm inserting
the phone number thought code in the Detail Format event as it's part of
other text in a letter. 
 
 
Does anyone know how to do this?
 
MTIA
 
Rocky