Can I use the tools on a phone or tablet?

The tools run in a mobile browser, but honestly they're designed for a laptop or desktop. The Cover Maker's editing (dragging art, placing the barcode, fine-tuning the spine) and the Interior Formatter's settings really want a larger screen and a pointer.

A good split:

• Do the work — building the cover, formatting the interior — on a computer.
• A tablet is fine for reviewing a preview PDF or checking an EPUB.
• A phone is best for quick things: checking your purchases in My Books, or reading these help articles.

Remember that work saved on one device stays on that device unless you download the project file and move it.