“def french_phone_number? (phone_number)” Ответ

def french_phone_number? (phone_number)

^
    (?:(?:\+|00)33|0)     # Dialing code
    \s*[1-9]              # First number (from 1 to 9)
    (?:[\s.-]*\d{2}){4}   # End of the phone number
$