Is phone function

functions.php

<?php 

function isPhone($val){
    if (!preg_match('/^((8|\+7)[\- ]?)?(\(?\d{3}\)?[\- ]?)?[\d\- ]{7,10}$/iu', $val))
        return false;

    return true;
}

//allow
/*
+79261234567 
89261234567 
79261234567 
+7 926 123 45 67 
8(926)123-45-67 
123-45-67 
9261234567 
79261234567 
(495)1234567 
(495) 123 45 67 
89261234567 
8-926-123-45-67 
8 927 1234 234 
8 927 12 12 888 
8 927 12 555 12 
8 927 123 8 123
*/