It seems like a bootloop.
Your iphone have problem with the new update, you can download a diffrent version of ios and downgrade it. The new update maby have a problem, and apple will fix it in time, until then you can try do plug your iphone to ituns, go to recovery and download a older version of ios. Like if you have ios 11.3 you see if you can download ios 11.1 or 11.2 and see if your problem is solved.