Document/Builder/DocumentBuilder.php
protected function formatPhoneNumber(PhoneNumber $number = null)
    {
        if ($number) {
            return $this->phoneNumberUtil->format($number, PhoneNumberFormat::INTERNATIONAL);
        }

        return null;
    }
protected function formatPhoneNumber(PhoneNumber $number = null)
    {
        if ($number) {
            return $this->phoneNumberUtil->format($number, PhoneNumberFormat::INTERNATIONAL);
        }

        return null;
    }
Formats the given phone number.

@param PhoneNumber $number

@return string