Isn't that only a vBulletin option? I'm looking at one of the forums I admin and I'm not seeing an option in phpBB 2.0.6 (and this is 2.0.5)
I think an upgrade would be in order when one fines the time though, in 2.0.6 the cookies work so the forum actually remembers who logged in, and the login control isn't as buggy as it is in this version.
If there is a mod for quick reply for phpBB I also agree, it works well, it's sweet and easy.