SUPER EASY QUESTION, super thankful if can be answered....

I'm looking to create a website, just a discussion forum really with minimal traffic. I've done this before using 1on1 webhosting service and found it really easy. However, with the evolution of the cell phone and people not jumping onto their PC as much, what format could I put this forum in that could easily convert to an app. Or is this super expensive?

I have to believe there is a software out there that can simplify forum access through an app rather than having to use a phone's browser.

What format would be best? That is I guess my question.

Thanks in advance.