I don't know which class/library you are using but here is the one that allows you to zip all files present in specified directory:
Create Zip File class
Usage:
$fileToZip="License.txt";
$fileToZip1="CreateZipFileMac.inc.php";
$fileToZip2="CreateZipFile.inc.php";
$directoryToZip="./"; // This will zip all the file(s) in this present working directory
$outputDir="/"; //Replace "/" with the name of the desired output directory.
$zipName="test.zip";
include_once("CreateZipFile.inc.php");
$createZipFile=new CreateZipFile;
//Code toZip a directory and all its files/subdirectories
$createZipFile->zipDirectory($directoryToZip,$outputDir);
$rand=md5(microtime().rand(0,999999));
$zipName=$rand."_".$zipName;
$fd=fopen($zipName, "wb");
$out=fwrite($fd,$createZipFile->getZippedfile());
fclose($fd);
$createZipFile->forceDownload($zipName);
@unlink($zipName);
Just specify the correct path to variable $directoryToZip
and all files in it will be zipped.