you shouldn't try to open phpbb actually inside wp page.
the best way to do it is to simply create a link to your board using the tab or whatever your menu has.
then, the board will simply open a page either replacing the one they were on or opening a new window. you can code the link for either method.
I am available for custom work on a donation basis. Please send me a PM with your needs.
Premium phpBB 3.2 Styles
OK, so what's the speed of dark?