How to form the body of a letter or how to substitute variables into an already formed letter?

Question

PHP

Hello! I have a self-written project in which I connected phpmailer, I have a task when registering a new user to the mail, to poison his registration data. Now my body of the letter is formed in a variable and the data is substituted (see screenshots)
I would like to make the letter in a separate file and I would take it with a function, for example file_get_contents and there were already substituted values, well, something like this, and not like now the entire letter is in a variable.
1 screen
screen 2

Answer 1

And what's the problem?
If there is no template engine, then ob_get_contentshelp.
php.net/manual/ru/function.ob-get-contents.php
Primitive example:

<table>
    <tr>
        <td><?= $variable_1 ?></td>
    </tr>
    <tr>
        <td><?= $variable_2 ?></td>
    </tr>
</table>

$mail = new PHPMailer();
$variable_1 = "Привет";
$variable_2 = "Чухча";

ob_start();
require_once("template.php");
$body = ob_get_contents();
ob_end_clean();

.....
$mail->Body = $body;
.....