http://mponpsecu5qaqu4s7chzbldsp6hu45pwecvr72m26xbf6lo3slqo6tad.onion/docs/INSTALL.html
If you do not have shell access or do not wish to use it, you will need to decompress the phpBB archive to a local directory on your system using your favourite compression program, e.g. winzip, rar, zip, etc. From there you must FTP ALL the files it contains (being sure to retain the directory structure and filenames) to your host.