I have a form with some data and 2 input for upload image, I have already read other questions on the site, but there are really many answers. I need only to reduce the size of the image before the upload to be faster for the user. what I can not understand is how to reduce the image and retrieve it from the mailer.php.  
<?php
    $nome        = $_POST["nome-locale"];
    $email       = $_POST["email"];
    $telefono    = $_POST["telefono"];
    $indirizzo   = $_POST["indirizzo"];
    $civico      = $_POST["civico"];
    $citta       = $_POST["citta"];
    $provincia   = $_POST["provincia"];
    $cap         = $_POST["cap"];
    $titolare    = $_POST["titolare"];
 $cf          = $_POST["codice_fiscale"]; 
    $declaration = isset($_POST["declaration"]) ? $_POST['declaration'] : 'No';
    $newsletter  = isset($_POST["newsletter"]) ? $_POST['newsletter'] : 'No';
    $data        = date('d-m-Y'); 
    $body = "<br>nome-locale:" . $nome . "<br>Email:" . $email . "<br>TelefonoLocale:" . $telefono . "<br>Indirizzo:" . $indirizzo . "<br>Civico:" . $civico . "<br>Città:" . $citta . "<br>Provincia:" . $provincia . "<br>Cap:" . $cap . "<br>Nome titolare:" . $titolare . "<br>CF:" . $cf . "<br>Declaration:" . $declaration . "<br>newsletter:" . $newsletter;
    use PHPMailer\PHPMailer\PHPMailer;
    use PHPMailer\PHPMailer\Exception;
    require 'PHPMailer/src/Exception.php';
    require 'PHPMailer/src/PHPMailer.php';
    require 'PHPMailer/src/SMTP.php';
    // Instantiation and passing `true` enables exceptions
    $mail = new PHPMailer(true);
    $mail->isSMTP(); // Send using SMTP
    $mail->Host       = x // Set the SMTP server to send through
    $mail->SMTPAuth   = true; // Enable SMTP authentication
    $mail->Username   = 'x // SMTP username
    $mail->Password   = 'x; // SMTP password
    $mail->SMTPSecure = 'ssl'; // Enable TLS encryption; `PHPMailer::ENCRYPTION_SMTPS` also accepted
    $mail->Port       = 465; // TCP port to connect to
    if (array_key_exists('menu1', $_FILES) && array_key_exists('menu2', $_FILES)) {
        try {
            //Server settings
            // First handle the upload
            // Don't trust provided filename - same goes for MIME types
            // See http://php.net/manual/en/features.file-upload.php#114004 for more thorough upload validation
            $menu1_filename = $_FILES['menu1']['name'];
            $menu2_filename = $_FILES['menu1']['name'];
            $menu1 = tempnam(sys_get_temp_dir(), hash('sha256', $menu1_filename));
            $menu2 = tempnam(sys_get_temp_dir(), hash('sha256', $menu2_filename));
            if (move_uploaded_file($_FILES['menu1']['tmp_name'], $menu1) &&
                move_uploaded_file($_FILES['menu2']['tmp_name'], $menu2)) {
                // Upload handled successfully
                // Now create a message
                //Recipients
                $mail->setFrom('feed@vaimenu.it', $data);
                $mail->addAddress('feed@vaimenu.it'); // Add a recipient
                $mail->isHTML(true); // Set email format to HTML
                $mail->Subject = ('Iscrizione: ' . $nome);
                $mail->Body = $body;
                $mail->AltBody = 'Iscrizione ricevuta da landing page';
                // Attach the uploaded file
                $mail->AddAttachment($menu1, $menu1_filename);
                $mail->AddAttachment($menu2, $menu2_filename);
                $mail->send();
                $mail->ClearAllRecipients();
                $mail->clearAddresses();
                $mail->ClearAttachments();
                $mail->isHTML(true);
                $mail->Subject = ('Benvenuto, ' . $nome);
                $mail->setFrom('feed@vaimenu.it', 'Vaimenu.it');
                $mail->addAddress($email);
                $message = file_get_contents('Benvenuto.html');
                $message = str_replace('%Nome%', $nome, $message);
                $mail->MsgHtml($message);
                if (!$mail->send()) {
                    $response['error']   = true;
                    $response['message'] = "Message could not be sent. Some thing went wrong Mailer Error: " . $mail->ErrorInfo;
                } else {
                    $response['success'] = true;
                }
            } else {
                $response['error']   = true;
                $response['message'] = 'Failed to move file to ' . $menu1;
            }
            echo json_encode($response);
        } catch (Exception $e) {
            $response['error']   = true;
            $response['message'] = "Message could not be sent. Mailer Error: {$mail->ErrorInfo}";
            echo json_encode($response);
        }
    }
?><form role="form" method="post" id="myform" action="mailer.php" enctype="multipart/form-data" >
.......
.......
<div class="form-group was-validated">
        <label class="control-label">Menu1</label>
        <input type="file" name="menu1" accept=".jpg,.jpeg,.pdf,.png" required>
       </div>
       <div class="progress">
        <div class="progress-bar progress-bar-striped progress-bar-animated" role="progressbar" style="width: 0%" aria-valuenow="100" aria-valuemin="0" aria-valuemax="100"></div>
       </div>
       <br>
                          <div class="form-group was-validated ">
       <label class="control-label">Menu2</label>
        <input type="file" name="menu2"  accept=".jpg,.jpeg,.pdf,.png" required>
       </div>
       <div class="progress">
        <div class="progress-bar progress-bar-striped progress-bar-animated" role="progressbar" style="width: 0%" aria-valuenow="100" aria-valuemin="0" aria-valuemax="100"></div>
       </div>
              
              
              ....
              <button class="btn btn-success btn-lg fa-pull-right" type="submit">Finito!</button>
              </form>