以下代码，测试可用。
//by www.qzphp.cn
$str = '13525462555';
$pattern = '/(\d{3})(\d{4})(\d{4})/i';
$replacement = '$1****$3';
$resstr = preg_replace($pattern, $replacement,$str);
echo $resstr;输出：
//by www.qzphp.cn 135****2555
以下代码，测试可用。
//by www.qzphp.cn
$str = '13525462555';
$pattern = '/(\d{3})(\d{4})(\d{4})/i';
$replacement = '$1****$3';
$resstr = preg_replace($pattern, $replacement,$str);
echo $resstr;输出：
//by www.qzphp.cn 135****2555
