Chosen Solution
My iphone frequently freeze then turns black.
Software problems can cause an iPhone to shutdown randomly. Try closing other apps and close any open tabs you might have open in safari/other browsers. If your iPhone’s storage is almost full, try deleting some info/apps off the device until you free up at least 10% of the total device storage. It is a good idea as well to back-up and reset the device software to rule out any additional software problems.
First check out phone detect on dfu mode or not via iTunes.If PC detect the phone restore it .If not try to force DFU mode.Finally if all fails that must be hardware issues.
Has your phone had water dmg in the past? Most likely a battery replacement
