function addCustomer($fname, $lname, $address, $phone) {

      $db = new MyDB();
      if(!$db){
         echo '<script type="text/javascript">alert("'.$db->lastErrorMsg().'");</script>';
      } else {
         //echo "Opened database successfullyn";
      }

      $sql ='INSERT INTO CUSTOMERS (FIRSTNAME, LASTNAME, ADDRESS, PHONE) VALUES ("'.$fname.'", "'.$lname.'", "'.$address.'", "'.$phone.'");';
      $db->query($sql);
   }

<?php
         require_once "queryDb.php";
         $firstname = $_POST["firstname"];
         $lastname = $_POST["lastname"];
         $address = $_POST["address"];
         $phone = $_POST["phone"];

        ?>

<form action="reviewsubmit.php" method="post">
  Test Address
  <input type="text" id="address" name="address" placeholder="test">  />
  Test phone
  <input type="text" id="phone" name="phone" placeholder="test">  />
  <input type="submit" name="Submit" value="Submit" />
</form>