Since my imagination layers on top of my existing senses, I wonder if aphantasia is really about the (in)ability to induce sensory hallucinations at will (and to what extent). That's about the only way I can make sense of it personally, given my own subjective experience.
Sound is like images for me. An abstract concept you can reason about later but only experience in the moment.
Maybe it "looks" like a comic with only speech bubbles. It's still not the right image, because there is no image, but it also doesn't feel like a total void.
Instead of a picture of a forest and some cracking of wood, I just have these words in my head and not the real picture/sound.
Same for every other sense.
The difference is that a book is already in a format I don't need to convert (to images) anymore.
About the 3x: if I need to show someone something to read on a screen and need to wait to scroll to the next page, I just read it 3 times and scroll then, it normally fits a "normal" reading speed.