While the tool itself is not mobile friendly, its launcher (“kindle-it”) and instructions are. That is, except the bookmarklet’s installation. Mobile browsers can’t install bookmarklets from links and that’s the only way you provide.
Can you change this behavior? The easiest solution is - in mobile mode (which, again, the instructions do have) - put the link inside a textarea with a copy button and instruct to bookmark the page itself, then edit it and paste the link.
The current workaround is not so user friendly. One has to think to long press the link to copy it, then bookmark the page itself and edit the bookmark’s link to paste the code.