<?php
$zip = new ZipArchive();

// open archive 
if ($zip->open('my-archive.zip', ZIPARCHIVE::CREATE) !== TRUE) {
    die ("Could not open archive");
}

// initialize an iterator
// pass it the directory to be processed
$iterator = new RecursiveIteratorIterator(new RecursiveDirectoryIterator("FolderI/"));

// iterate over the directory
// add each file found to the archive
foreach ($iterator as $key=>$value) {
    $zip->addFile(realpath($key), $iterator->getSubPathname()) or die ("ERROR: Could not add file: $key");
}

// close and save archive
$zip->close();
?>