Welcome. In regards to an app, the only one involving forums that i'm familiar with is tapatalk but i'm not sure if it supports this particular board.
I assume you're using the "mobile version" of this forum in your phone's browser? If that is the case, have you tried viewing the forums and setting your phone's browser to "Desktop Mode"? Desktop mode let's you view the forum the same as you would if you were using a PC/laptop. Sometimes an android browser app won't always force desktop mode even if you enabled it, in that case I download a decent lightweight browser like Dolphin, Brave or Opera which usually successfully force desktop view via an option in the settings.
Maybe you prefer the streamlined versions of forums but in my experience I find that most "mobile version" of any website is a pain because it doesn't offer all of the forum's features and/or simply just has a poor/clunky design. Desktop mode may be awkward at first but the only drawback i've found is rarely you may need to zoom in a bit to click a tiny button/link/object.