$tel = '010-1234-5678';
echo preg_replace('/(\d{3})(-?)(\d{2,})(-?)(\d{4})$/','\1\2****\4\5',$tel);
echo "\n";
$tel = '01012345678';
echo preg_replace('/(\d{3})(-?)(\d{2,})(-?)(\d{4})$/','\1\2****\4\5',$tel);
echo "\n";
------=-----------
$ php b.php
010-****-5678
010****5678