How to put the execution of the php script through the form?

Question

PHP

Good afternoon! Let's get straight to the point:
There is this code:

<form action="mail/mail.php" method="post" >
                        <div class="input-dark">
                           <i style="font-size:24px" class="fa">&#xf095;</i>
                            <input type="text" name="phone1" value="" placeholder="Введите номер телефона" data-mask="phone" />
                        </div>
                        <input type="submit" value="Получить расчет" />
                    </form>

When filling out the form and submitting it, the php script is executed:

<?PHP
    $phone = $_POST['phone1'];

    
   $phone = htmlspecialchars($phone);


   $phone = urldecode($phone);

  
   $phone = trim($phone);

  
mail("[email protected]", "Новая заявка", " Телефон: ".$phone.") or die("Error");

header('Location: https://i.imgur.com/yTjeLaN.jpg');
?>

It seems that everything should work, but after filling out the form and sending it, it redirects to an empty page domain/mail/mail.php (directory of the script itself)
What could be the problem? Tell good people)