I think what you are seeing is what’s called multiplexing: the screens aren’t all lit up at once, the are lit up in sections one after the other in very fast succession, this makes it so you can make the control circuit smaller by reducing the number of segments it needs to drive
Your phone camera has a frame rate that likely won’t match the multiplexing frequency, this means that in every frame a different segment will be lit, so it looks all flashy
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