There are a lot of phpbb plugins that forum owners can install to deliver a mobile version of their forums. In researching the various methods for implementing a phone-compatible version of our forum, Tapatalk was one of the most elegant, robust and simple-to-install solution we came across. I would have, of course, preferred that the actual app was free for all of the forum users, but I guess that is the trade-off.
While not ruling out a phpbb add-on of some sort to deliver up a mobile version of the site at some point in the future, we have done significant customizations to our forum, and sometimes add-ins don't play nice in customized phpbb installs.
So for now, you can access the whole ftlop site & forum on your phone using the built-in browser (just as you would do on a pc), or use the tapatalk app to access a light, but fully functional, version of the forum.