That phone seems to have a proprietary operating system, so it's possible it could be limitations of the programming itself.
If you are unable to set vibrate only from the basic menus and options, the only other way would be to induce phone hacking with tools created by other users.
If you want to be able to adjust customization to your own preference on anything phone related, it's better to stick to one where a popular o/s is on it. That would include android, iphone os, or blackberry os. With everything else it's just hit or miss.