Using global variables in PHPMailer

Question

Instead of this:

$mail->isSMTP();  
$mail->Host = 'smtp.demo-server.com';
$mail->SMTPAuth = true;
$mail->SMTPSecure = PHPMailer::ENCRYPTION_SMTPS;
$mail->Port = 'demo-port';
$mail->Username = '[email protected]'; 
$mail->Password = 'demo-password';

I would like to keep the values in a separate file and use variables instead:

$mail->isSMTP();  
$mail->Host = echo $server; // also tried without echo
$mail->SMTPAuth = true;
$mail->SMTPSecure = PHPMailer::ENCRYPTION_SMTPS;
$mail->Port = echo $port;
$mail->Username = echo $username; 
$mail->Password = echo $password;

I'm already using output buffering, have set the global scope, and the variable values contain the quotes. Still not working.