As others already suggested, you can enable the "less secure" applications or you can simply switch from ssl
to tls
:
$mailer->Host = 'tls://smtp.gmail.com';
$mailer->SMTPAuth = true;
$mailer->Username = "[email protected]";
$mailer->Password = "***";
$mailer->SMTPSecure = 'tls';
$mailer->Port = 587;
When using tls
there's no need to grant access for less secure applications, just make sure, IMAP is enabled.