Considering the Black phone is in power saving mode - no surprise the screen has been dimmed by the OS.
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Calm down. It's a help forum. People come here for help and to learn new things. What better way for someone who doesn't know about auto-brightness than to ask a question like this on this forum.
Did you see the Ops phone? The icon layout is practically identical to the in store demo model - meaning either the Op has never felt the need to ever erase of move any icons for personal use - or is a newer user to iPhone and very well might not know how to swipe to check brightness and its auto settings.
As as I mentioned above the power saving feature would have probably dimmed the screen in this case with the battery at 5%.
If you have something constructive to help the Op, then let's hear it. Otherwise getting angry at those trying to help is just a waste of everyone's time. Yes, even yours.