Here is the quickest way how you can change the screen timeout or set auto-lock on your iPhone. Basically, your mobile will auto-lock itself after a certain time. However, sometimes this Auto-lock is grayed, but that is only because the lower power mode is on, turning it off will easily fix it.

We usually have it auto-lock fixed at 30 seconds, but again it really depends on the iPhone user. Some like the prompt closing of the phone while some chooses to manually lock or set it for a longer period of time. Regardless, here is quick access to change these settings.