When your phone is too bright at night

Me right now.

I'm still on iOS 8.4 but I learned you can set triple click to zoom except you set a dark filter and zoom X1 so you aren't actually zooming in but the screens a bit darker.

Or when your light sensor quits working.

I hiss at it till either my eyes adjust or the light turns down

Well, there are apps specifically for using your phone at night, which reduce the brightness a lot.