validate or format phone number in php

format_phone.php

/**
 * FormatPhone formats phone number
 * @param string $number phone number
 * 
 * @return int formatted phone number
 *
 */
function FormatPhone($phone)
{
    $rx = "/
            (1)?\D*     # optional country code
            (\d{3})?\D* # optional area code
            (\d{3})\D*  # first three
            (\d{4})     # last four
            (?:\D+|$)   # extension delimiter or EOL
            (\d*)       # optional extension
        /x";
    preg_match($rx, $phone, $matches);
    if(!isset($matches[0])) {
        return "the given number is not a valid phone number";
    }

    $area = $matches[2];
    $three = $matches[3];
    $four = $matches[4];

    return "$area$three$four";
}

validate_phone.php

/**
 * ValidatePhone validates phone number
 * @param int $number phone number
 * 
 * @return string error message if there's any
 *
 */
function ValidatePhone($number) {
    if (empty($number)) {
        return "There is no Phone number given. (UserController)\n";
    }
    // eliminate every char except 0-9
    $justNums = preg_replace("/[^0-9]/", '', $number);

    // eliminate leading 1 if its there
    if (strlen($justNums) == 11) $justNums = preg_replace("/^1/", '',$justNums);

    // if we don't have 10 digits left, let's say it's invalid.
    if(strlen($justNums) != 10) {
        return "Phone number is invalid. (UserController)\n";
    }
    return "";
}