You could also buy a pair of $8 orange safety goggles and a piece of orange cellophane to cover your phone. The frequencies that disrupt circadian rhythm are 500nm to 450nm or so with the strongest response at 470nm. Response is also dependent on duration and ambient light levels, so if you are in the dark, as much as 0.5 lux of blue light over an hour can halt your pineal gland from producing melatonin.
F.lux also shouldn't be relied upon by itself. How well it works is dependent on the particular frequencies emitted by the RGB components of your screen. I have a 470nm band pass filter that I look at light emitters through, and f.lux reduces such emitters, but doesn't stop them completely. I have constructed a removable orange filter as a supplement.
I actually have those goggles, but find they don't fit well over my glasses. Know of any pair designed to work with glasses?
I know flux isn't perfect. But as I don't really use my phone much before bed, it seems to work well enough. The glasses could be useful for late night computer work though.
There is a website that sells over the glasses shades for this purpose, but those are way over priced. Most anything orange stands a good chance of working. You can park an incandescent bulb behind one and look at its spectrum reflected off of a CD or DVD. Look for the blue that looks like the sky on a cloudless day. I'd buy over-glasses safety goggles from a store, then test them at home and return them until you found a pair that works.
For $24, you can get enough orange filter gel to make a filter for your 27" screen, then have enough left over for a couple of iPads and several iPhones.
Now, I could do one of the following:
I tried not using my phone for 1 hours before bed, still had insomnia. There's no trivial lifestyle fix that would address the issue f.lux solves.