Users type phone numbers however they like — dots, dashes, spaces, a leading 1, parentheses. That variety makes numbers impossible to search, deduplicate, or hand to an API. This pair of scripts normalises every number to (678) 800-1234 on save, and rejects anything that is not ten digits.

Before you start

One single-line field to validate — Phone_additional in this example. Rename it in both scripts to match your form. Nothing else is required.

Part 1 — the validation script

// Trigger: On Add / On Edit > On Validate
if(!isBlank(input.Phone_additional))
{
    digits = input.Phone_additional.replaceAll("[^0-9]","");

    // Tolerate a leading US country code
    if(digits.length() == 11 && digits.startsWith("1"))
    {
        digits = digits.subString(1,11);
    }

    if(digits.length() != 10)
    {
        alert "Phone number must be 10 digits. Received " + digits.length() + ".";
        cancel submit;
    }

    input.Phone_additional = thisapp.Update.PhoneFormat(digits);
}

Part 2 — the reusable function

Create this as a standalone function so any form in the app can call it. Keep the name Update.PhoneFormat and the script above works unchanged.

string Update.PhoneFormat(string phonefield)
{
    digits = phonefield.replaceAll("[^0-9]","");
    if(digits.length() != 10)
    {
        return phonefield;      // hand back untouched rather than throw
    }
    return "(" + digits.subString(0,3) + ") " + digits.subString(3,6) + "-" + digits.subString(6,10);
}

Notes

• Why the function re-strips the digits. It is defensive: called from elsewhere with raw input, it still behaves. A helper that only works when its caller has already cleaned the data is a helper that breaks the first time someone else uses it.
• It returns the input untouched on a bad length rather than throwing. A formatting helper should not be able to take down a form.
• On Validate, not On Success. On Validate can still cancel the save. By On Success the record is already written.
• International numbers. This is US and Canada only by design. For anything global, do not pattern-match — use a validation service, such as the Neutrino script elsewhere in this section.