Login into your FTP Server and goto the root directory where you want to create archieve of the folder.
create a file called zipper.php in your local server and write this code below-
$archive = “xyz.zip”;
$directory = $_SERVER[‘DOCUMENT_ROOT’];
exec( “zip -r $archive $directory”);
Now upload this zipper.php file in the same directory and run the url of the file. If your website is say http://example.com, then goto http://example.com/zipper.php then it will create a archieve of the whole directory named xyz.zip