Agreed. You're getting the advice to "create an application" because that's what the Google Play store is listing and giving users access to: Applications they can download to their Android phone.
You're correct that phpBB "is already an application"; but it's a PHP application that runs under Linux, Windows or other web server operating systems. It's not an Android application that downloads to your phone; nor is it intended to be.
When you have a phpBB forum -- such as phpbb.com/community
-- you do not need Android users to "install a new application your Android device doesn't currently have" in order to access that forum. You just need those users to open this web site URL in whatever web browser the user prefers & already has installed on their device. I suspect if you asked Google, they would say helping users find your web site address "is what google.com is used for, not the Google Play store."
That doesn't mean you can't
create an application, and then do the work to get this application listed & maintain that listing in the Google Play store. But your application "isn't going to do anything" other than open your site in whatever web browser is already installed on the device. I don't know if Google Play even allows such applications, but that's the kind of thing you're talking about.
If that sounds like something which would be helpful to you and worth the time to pursue, then you want to discuss the simplest way to achieve this in a Google Android application development group like David recommended. i.e. "I want to create an application that just opens my web site, so that users searching Google Play for keywords related to my site will find this application."