function mobileReplace($mobile,$start,$end,$str="*"){    $countStr = abs($end-$start);    $replaceStr = $str;    for($i=0;$i<$countStr;$i++){        $replaceStr.= $str;    }    $mobile = substr_replace($mobile, $replaceStr, $start-1, $countStr+1);    return $mobile;;}

　　

$mobile = '13188888888'; echo mobileReplace($mobile,4,7); //132****8888