Phone formats
Phone number formatting for test data
A country calling code, a presentation mask, and a valid phone number are different things.
Store a canonical representation
For systems that handle phone data, use a documented international representation such as E.164 when it is appropriate for the product. Apply local spacing and grouping only for display.
Keep test values non-routable
A plausible-looking number can still reach someone. Use a deliberately invalid value or an environment-specific test range, and do not treat a format mask as a validation rule.
Data provenance