Check valid vietnamese mobile phone number

check.php

<?php

function format_vn_phone($phone)
{
	$phone = preg_replace('/[^0-9]/', '', $phone);
	if (strlen($phone) > 10 && substr($phone, 0, 2) == '84') {
		$phone = substr($phone, 2);
	}
	
	return substr(empty($phone) || $phone[0] == '0' ? $phone : '0'.$phone, 0, 11);
}

function is_valid_phone($phone)
{
	$phone = format_vn_phone($phone);
	$match = preg_match('/09\d{8}|01(20|21|22|23|24|25|26|27|28|29|62|63|64|65|66|67|68|69|86|88|99)\d{7}/', $phone);
	return $match ? $phone : false;
}