PHPMailer not working when function is within and included file - phpmailer

Question

Something is mighty odd. I created a basic test file with the code from PHPMailer.
# Import the PHPMailer class into the global namespace
use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\SMTP;
use PHPMailer\PHPMailer\Exception;
require 'includes/PHPMailer/PHPMailer.php';
require 'includes/PHPMailer/SMTP.php';
require 'includes/PHPMailer/Exception.php';
function sendCampaignEmail ($email, $firstname, $lastname)
{
$mail = new PHPMailer(true); // Create a new PHPMailer instance. Passing `true` enables exceptions.
try {
//Server settings
# $mail->SMTPDebug = SMTP::DEBUG_SERVER; // Enable verbose debug output. SMTP::DEBUG_SERVER = client and server messages
# $mail->SMTPDebug = SMTP::DEBUG_CLIENT; // SMTP::DEBUG_CLIENT = client messages
$mail->SMTPDebug = SMTP::DEBUG_OFF; // SMTP::DEBUG_OFF = off (for production use)
$mail->isSMTP(); // Send using SMTP
$mail->Host = 'myhostxxxx.co.uk'; // Set the SMTP server to send through
$mail->SMTPAuth = true; // Enable SMTP authentication
$mail->Username = 'oobaclub#xxxxxxxxx.co.uk'; // SMTP username
$mail->Password = 'xxxxxmyEmailPasswordxxxxx'; // SMTP password
$mail->SMTPSecure = PHPMailer::ENCRYPTION_SMTPS; // Enable TLS encryption; `PHPMailer::ENCRYPTION_SMTPS` encouraged
$mail->Port = 465; // TCP port to connect to, use 465 for `PHPMailer::ENCRYPTION_SMTPS` above
//Recipients
$mail->setFrom('myfromemail.co.uk', 'My Name');
$mail->addAddress($email, $firstname . ' ' . $lastname); // Add a recipient
$mail->addReplyTo('myfromemail.co.uk', 'My Name');
// Content
$mail->isHTML(true); // Set email format to HTML
$mail->Subject = 'Here is the subject';
$mail->Body = 'Dear ' . $firstname . ' ' . $lastname . '<br/><br/>This is the HTML message body <b>in bold!</b>';
$mail->AltBody = 'This is the body in plain text for non-HTML mail clients';
$mail->send();
echo '<br/>Message has been sent to ' . $email . ' (' . $firstname . ' ' . $lastname . ')';
} catch (Exception $e) {
echo "Message could not be sent. Mailer Error: {$mail->ErrorInfo}";
}
}
$names= array();
$id=0;
$names[$id]['email'] = "atestemail#gmail.com";
$names[$id]['first_name'] = "Bob";
$names[$id]['last_name'] = "gMail"; $id++;
$names[$id]['email'] = "anothertest#testingmyemail.co.uk";
$names[$id]['first_name'] = "Sid";
$names[$id]['last_name'] = "Smith"; $id++;
$count=0;
while ($count < count($names))
{
sendCampaignEmail ($names[$count]['email'], $names[$count]['first_name'], $names[$count]['last_name']);
$count++;
}
THIS CODE ABOVE WORKS FINE.
So... Then, I took the function and put it into an Included file (where all my functions are: "globalfunctions.php").... And now it says "Fatal error: Uncaught Error: Class 'PHPMailer' not found"
So, now, at the top of my index.php, I have:
## PHP MAILER - # Import the PHPMailer class into the global namespace
use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\SMTP;
use PHPMailer\PHPMailer\Exception;
require_once 'includes/PHPMailer/PHPMailer.php';
require_once 'includes/PHPMailer/SMTP.php';
require_once 'includes/PHPMailer/Exception.php';
require_once 'includes/connect.php';
require_once 'includes/globalfunctions.php';
I am confused as everything else works. All my other functions work. I thought namespaces were global... But, I tried adding the "use" code into the function... but, as expected, that didn't work either....
I am stumped.

Answer 1

PHP use declarations are local aliases that apply only to the file they appear in. You have to add a use statement in every file that uses that class; you can't put all your declares in one file and then include it from somewhere else.
Now might be a good time to learn how to use composer as it takes care of a lot of this.