I have heard a number of people say that they started to have trouble with maths problems once they got abstract enough to be unvisualisable. So I credit my ability to do complex abstract maths with the fact that I have had to use non-visual strategies right from day 1.
Of course, this only works if complex abstract maths is a thing in your life!
Phollowing phosphenes is a good path to going to sleep.
If you can damp down other thoughts and go with the dots and swirls your brain will stop troubling you.
Lying in bed with eyes close is also a great time to try to visualize things.
You know where you are laying, which direction you are facing how many feet off the various walls and floors are. Try to imagine exact what will appear before your eyes when you open them. Open your eyes and see how far you are off. Often it’s by quite a lot, but you can get better at it, if you’re in a familiar, stable environment. Listening helps too. We humans do more echo-location than we’re willing to admit.
A visualization is not, and will never be a phosphene. I’ve tried making phosphene generators that’ll put out circles and squares. Be a lot of fun if possible. Lots of people have tried; patents and such. As far as I can tell, no one has succeeded.
Dreams are definitely what you call image streaming, although there’s taste and smell and touch streaming too. Phosphenes appear to be fundamentally abstract. That, or the interface is to complex for us to mess with in any meaningful way.