Not clear what do you mean by this. Normally, a client connects to the server. As to Filezilla, this is a two-part software: an FTP/SFTP/FTPS server and a client:
http://en.wikipedia.org/wiki/Filezilla[
^].
I never knew that Filezilla client part could act as a server. I also never saw a PHP API for the Filezilla client; even if it does exist, I never heard of it.
So, if you want to "connect" to Filezilla client part, I don't know what it supposed to mean. However, if you want to connect to Filezilla server, you can always do it, but, first, you will need a PHP FTP client, and, second, then it would not matter if you are using Filezilla or not; it would work for any valid FTP server.
If this is what you want, you can find a suitable PHP FTP client. Please see:
https://github.com/suin/php-ftp-client[
^],
http://freecode.com/projects/asukphpftp[
^],
http://webscripts.softpedia.com/script/Internet-Browsers-C-C/FTP/PHP-FTP-Client-42153.html[
^].
Try to find some more if you need:
http://lmgtfy.com/?q=FTP+client+PHP[
^].
Good luck,
—SA