The expression you entered is called "regular expression" and it technically represents the description of the pattern of characters that constitute a valid US phone number. There is no provision to use regular expressions in the QuickBase formula language or form rules. You can however use regular expressions with JavaScript to validate a field. However to do this you need to set up a JavaScript injection technique such as the IOL techinique. to get the JavaScript into the form in the first place. Additionally, you need to decide what feedback you want to provide to the user as the JavaScript can detect and report errors in the phone number (1) on a key-by-key basis, (2) when the field blurs, or (3) when the form is about to submit. Any of this is possible but you have to use script.
