iPhone 8 plus stuck on loading screen
Because I am new to Stack Exchange, I am unable to ask a followup question as a comment. I am aware that I am not to ask these kinds of questions in a reply, so I am going to make some assumptions about this situation. If any of these are false, let me know and I'll reconsider.


I am assuming you were not doing an update when the iPhone froze. If you were doing an update, you may have some other issues. I would like to know what iOS version you are running, but I can live without that info.
I know you mentioned the steps of hard rebooting, but it sounds like the reboot was not successful. I apologize if I have misinterpreted this. That being said, hard reboot this phone. For iPhone 8, hard rebooting is a bit different than in other iPhones. After hard rebooting, you may encounter the loading screen again, but it should start loading. Please follow these instructions
Please note that one hard reboot may not work, but three hard reboots in quick succession (meaning when you see the Apple logo appear, hard reboot again immediately) can cure a LOT of software problems. Also note that it is entirely possible that this is a fluke. I work as an iPad specialist for a school corporation, and I have noticed on several occasions that three hard reboots have solved some unusual iOS issues. 
If the three hard reboots still fail, please try another hard reboot and hold in the side switch to force a "connect to iTunes" message (information about doing that can be found on the same link I mentioned earlier). Plug iPhone into a computer, and have iTunes update the software (if it hasn't already).


Good luck!