Most iPhones have a sensor on the power/flash flex called the mic2 sensor that will cause the phone to boot loop in three minute intervals if that sensor fails. I figure once you get into the panic logs, there's probably about a 90% chance you'll see a line saying something like, "missing sensor: mic2". Once you replace that cable, that should fix your boot loop issue.
Alisha (@flannelist) has written our definitive guide to kernel panics and it's definitely worth a look.
[[iPhone Kernel Panics|iPhone Kernel Panics - iFixit|new_window=true]]
Assuming you are on a three minute reboot cycle, that's actually long enough to get in and catch a screenshot of the first page of the panic log, which is really all we need to verify the cause.