Screen brightness issues

My screen contrast will darken from brightest (my default setting) down 2 to three levels on its own. Sometimes after the screen darkening several levels, it will brighten 1 level. I notice this happening when phone is charging and the back of my phone feels warm. Also, this will happen in the Summer time. It seems like heat may be a factor. I have tried all possible solutions to correct the screen issue and none have work for very long. I previously had the iPhone 8 pro plus which never had any issues. I believe the problem is inherently a device hardware issue. This problem is very frustrating given the fact that this phone is not cheap. Any solutions will be helpful. I am considering taking this phone back to Verizon out sending this phone back to Apple. Thank you