PHP - Simple Rotation

I have some photos that were taken using a cellphone in an upright/vertical position.

They were downloaded and placed in a folder to be viewed on a webpage but they displayed horizontally/sideways (with the persons head on the left).

I am assuming that the EXIF information in the image tells it which side is up and what the intended 'top' of the picture should be..

I want to have a PHP function that will rotate the image to its intended display position so that photos of mountain ranges [intentionally holding the smartphone sideways] are horizontal and portraits [where the smartphone in upright] are vertical.

I placed this code in a PHP file but got no change in the image:

function correctImageOrientation($filename) {
  if (function_exists('exif_read_data')) {
    $exif = exif_read_data($filename);
    if($exif && isset($exif['Orientation'])) {
      $orientation = $exif['Orientation'];
      if($orientation != 1){
        $img = imagecreatefromjpeg($filename);
        $deg = 0;
        switch ($orientation) {
          case 3:
            $deg = 180;
            break;
          case 6:
            $deg = 270;
            break;
          case 8:
            $deg = 90;
            break;
        }
        if ($deg) {
          $img = imagerotate($img, $deg, 0);        
        }
        // then rewrite the rotated image back to the disk as $filename 
        imagejpeg($img, $filename, 95);
      } 
    } 
  } 
}

$filename = 'upload/myTest.jpg';

correctImageOrientation($filename);

Am I using the correct approach to get the desired result?

Is the code correct?

I have several images created with a Kodak electronic camera and my iPhone. All images are displayed with the correct orientation (portrait or landscape) in  the HTML code. The HTML code is wrapped inside a brief PHP code to enable password entry, and the PHP code is uploaded to my Web site along with the images.

I have examined the images on my Web site using Web browsers in Windows 10 and Apple MacBook Air. The orientation is incorrect for at least one of the images in each browser -- Internet Explorer, Firefox, Chrome and Safari. Although a majority of the images are oriented correctly, incorrect rotation occurs for some of the phone and Kodak images.

I shall provide more information to anyone who can  provide me with help and suggestions, which will be much appreciated.

Thank you

spruce18b