Ok, I checked it out. Everything works the same in mobile Safari as on computer except for the lists labeled 'Parcelas'. They look like empty menus instead of lists. You have to tap on them to see the list, which is then scrollable in the pop-up menu. Until you perform a calculation, they are empty, but they store each result.
You can even select the result and have them display as the menu choice. Weird.
Of the three other browsers I tried only Puffin displayed the page the same (or close enough) as the desktop. Since Puffin actually runs the page via a remote server using a desktop browser, I shouldn't be surprised. Other Flash enabled browsers will probably work as well.
Note, this is not because the page uses Flash, it is because the remote servers are running desktop versions of a web browser.
So, you can either use Puffin or something like, or just tap on the item to see the list instead of having it displayed automatically.