How to enable login section in php?

Enable login section in php

//redirect to dashboard if session is active code

session_start();
if(isset($_SESSION['ID'])){
dashboard();
}

//dashboard redirect code used in function.php

function dashboard(){
echo '<script LANGUAGE="JavaScript">window.location.href="'.site_url().'/dashboard/";</script>';
}


//php code

if(isset($_POST['login'])){

extract($_POST);



global $wpdb;
$table_name = $wpdb->prefix . "shopkeeper_signup";
$results = $wpdb->get_results("select * from $table_name where phonenumber LIKE BINARY '$phonenumber' and pass LIKE BINARY '$pass'");



foreach($results as $result)
{
$phone = $result->phonenumber;
}



if((count($results)) > 0 ){
session_start();                           //session started here
$_SESSION['ID']=$phone;
return dashboard();
}
else
{
$msg = "Username or Password is wrong!<br>click here to <a style='color:#FFEB3B' href=".site_url().">login</a> again";
}



}