Time will come
But you should not only seek for phpBB specialized directories.
phpBB is not necessarily the most important here as a common point. I'd say community based web sites are in general, and your project specific main topic in particular.
Once you are done with the major search engines directories and DMOZ, then, you should first look at the directories PageRank and rules, and then chose the best category and write down a well though description.
This is the mos important IMHO when it comes to directory submission.