Most people check their phone all day and then as soon as they get to bed...they scroll (I know I do!). Obviously that isn't good on your eyes PLUS it keeps your brain stimulated so that when you finally turn off your phone and try to sleep, your brain isn't ready to!
HOWEVER, there is a feature on your iPhone that helps prevent a lot of the negative effects from looking at your phone in the dark!
Since the backlight (or "blue light") of your phone tricks your brain into thinking it's still daytime and you should stay awake, switching your phone into Night Shift mode helps eliminate a lot of that blue light that makes you stay awake!
To activate it, swipe up on the home screen and hold down on the brightness button until the night shift option shows up!
You can even set it on a timer so if you want it to go on at 10pm every night, it will do it automatically!