Querying Data from MySQL via PHP

Question

Good afternoon. I'm teaching myself SQL and PHP, and have run into a roadblock. I imagine it's quite simple but of course I can't figure it out. I have a server running Apache2, MySQL, and PHP8.1. I need to host a local webpage that lists DB table information using the PDO method. I've written the HTML and PHP, but when running the PHP script within the HTML page, I get a blank space, and if I run the PHP script on its own, I get a 500 error. After looking at Apache logs, I've found that it's a 500 185 error, which I have learned is essentially a "too much to handle" error (but it's not). Here's my code:

  
  $servername = "[local IP:port]";
  $username = "[sql username]";
  $password = "[sql password]";
  $databasename = "labeling";
  
  // CREATE CONNECTION
  $conn = mysqli_connect($servername, 
    $username, $password, $databasename);
  
  // GET CONNECTION ERRORS
  if (!$conn) {
      die("Connection failed: " . mysqli_connect_error());
  }
  
  // SQL QUERY
  $query = "SELECT partnum, partdesc, colorant, material, quantity, monum, boxnum FROM `press01`";
  
  try 
  {
      $conn = new PDO(
        "mysql:host=$servername;dbname=$databasename", 
        $username, $password);
  
      $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
      $stmt = $conn->prepare($query);
      // EXECUTING THE QUERY
      $stmt->execute();
  
      $r = $stmt->setFetchMode(PDO::FETCH_ASSOC);
      // FETCHING DATA FROM DATABASE
      $result = $stmt->fetchAll();
      // OUTPUT DATA OF EACH ROW
      foreach ($result as $row) 
      {
          echo "Part #: " . $row["partnum"]. "Part Description: " . 
            $row["partdesc"]. "Color: " . $row["colorant"]. "Material: " .
            $row["material"]. "Box Quantity: " . $row["quantity"]. "MO#: " . $row ["monum"].
            "Box #: " . $row["boxnum"]. "<br>";
      }
  } catch(PDOException $e) {
      echo "Error: " . $e->getMessage();
  }
  
$conn->close();
  
?>

I expect to be given a list with the aforementioned values. What am I doing wrong? Forgive me, I'm still green with PHP.

After enabling error reporting, I'm met with the following:

Fatal error: Uncaught Error: Call to undefined method PDO::close() in /var/www/html/press01.php:55 Stack trace: #0 {main} thrown in /var/www/html/press01.php on line 55