Frankly, the easiest way to do it is to create it on your laptop or desktop and set things up so your bookmarks sync with your phone. You can do this with both Safari and Chrome, but Safari might be a bit trickier for your if you aren't on a Mac.
Note that the above will only create a Bookmarklet for your iPhone or iPad. Follow the main "Bookmarklet" instructions for one that you can use on your laptop or desktop.
Have more questions? Submit a request