Include Field Mask Characters in Form Fields

I am using a mask for a phone number such as “(999) 999-9999”. The mask works and formats the value properly, but I wanted to be able to add the characters “{ }” and space with the number entered. I see the options:

Field Mask
Validate with Mask

Can I use a PHP code block that can be executed as I hit the ENTER key to go to the next field to include the mask characters? If OI cannot could an option be added that includes Mask characters with the data I enter?