If it's a new phone that you haven't change anything (opening it) AND you have it less than a year, I recommend you to go to the Apple Store. This is because you still have the one year warranty that comes with the product. When you go, the technician will try updating your phone. If it fails to update, your phone will be replace.
I know this because my iPhone 6+ had the error. Since it was still under warranty, I brought it to the Apple Store and get it check out. They replaced my phone. So I got a new phone. I didn't pay anything because it was under warranty.
Just want to share to save you some trouble and get a brand new phone.