PhpBB is very good and very powerfull forum software. It is also very difficult to understand for newbies but once get used to it, it will become very easy.
I prefer Mybb more because it is also a very pwerfull software but its very easy even a newbie can get used to it in a couple of hrs.
phpBB was good, just not good enough. I started using it after it was the first result when I googled free forum software around 3 years ago. As soon as I tried MyBB it did everything phpBB didn't and just worked so much better.