I want to save this forum in my android phone so that I can read it in my spare time especially when I’m a way with my computer. Like facebook except you can browse it offline.
You can`t. There is a very huge database behind that you would need to read the forum offline.
If you don’t have to worry about data charges, just use your web browser ON your Android phone. You might see if the Tapatalk forum interface works, it may be more usable than the desktop-style web browser.