- var_dump: documentation ( source)
- mb_substr: documentation ( source)
- mb_strlen: documentation ( source)
- str_repeat: documentation ( source)
- ceil: documentation ( source)
<?php
$m = '13290052201';
$l = 5;
$f = ceil((mb_strlen($m)-$l)/2);
var_dump(mb_substr($m, 0, $f) . str_repeat('*', $l) . mb_substr($m, 0, mb_strlen($m)-$l-$f));