WHAT IS THE FORMULA
I’m not quite sure about what you meant. Would you please provide us with an example and further description to refer to?
INTERNATIONAL CODE OR COUNTRY CODE
IS THERE IS FORMULA TO ADD IN FIELDS
If you already have the international code or country code saved as field values, you may use the string formulas to combine the code and the phone number.
If you need support on how to write the formulas, please share a screenshot of your form design and share an example so that we could guide based on your needs.