@Monroe I actually don’t have f.lux on my iPhone. I mean in the control center there’s the screen brightness slider, and if I press and hold, i can access Night Shift, apple’s built-in blue light filter.
https://support.apple.com/en-us/HT207570
Back when I had my droid, I used an app called Nightowl, which would dim the screen further than android would normally let you, and filter the blue light. Android (at least version 6) doesn’t have such a feature automatically built in like apple does.
...but yeah, there’s a slider in f.lux to control the dimming, as you found out