The PHP ftp_mlsd() function returns the list of files in the specified directory.

<?php
// connect and login to FTP server
$ftp_server = 'ftp.example.com';

$ftp_conn = ftp_connect($ftp_server) or die('Could not connect to ' . $ftp_server);
$login = ftp_login($ftp_conn, $ftp_username, $ftp_userpass);

$dir = '/images';
$dirlist = ftp_mlsd($ftp_conn, $dir);

// output directory list
echo($dirlist);

// close connection
ftp_close($ftp_conn);
?>

// returns the list of files from the "images" directory

ftp_mlsd(ftp_conn, dir)