On iPhones released after the iPhone X there is a sensor on the charging port flex that communicates with the CPU. If this sensor is damaged or missing (as it may be on poor quality 3rd party parts), the device will reboot itself every 2 minutes and 50 seconds. Since you replaced the lightning port here I suspect this is the issue. To verify this issue you can check the panic logs (search "Analytics" in settings, look for a file called "panic-full-xxx.ips" under Analytics Data.
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On iPhones released after the iPhone X there is a sensor on the charging port flex that communicates with the CPU. If this sensor is damaged or missing (as it may be on poor quality 3rd party parts), the device will reboot itself every 2 minutes and 50 seconds if the screen is on (it won't reboot while locked). Since you replaced the lightning port here I suspect this is the issue. To verify this issue you can check the panic logs (search "Analytics" in settings, look for a file called "panic-full-xxx.ips" under Analytics Data).
See [post|651841|this question|new_window=true] for more information (different model, but same issue).
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The good news is that your phone is not toast and you haven't done anything irrepairable, the bad news is that you will probably need to replace your charging port again.
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As for the other issues you mentioned: the phone will function perfectly fine if you forgot one of the screws for the bracket. It's best to put everything that was in the phone back the way it was but one missing bracket screw is not the end of the world and shouldn't cause issues. Regarding the charging coil, you can check whether the phone wireless charges still. If it does you're all good. Small scrapes to the black part should not affect the functionality. If the flex was torn or the part where the flex is soldered to the pad was damaged or disconnected, then wireless charging may be affected. However neither of these issues will cause the rebooting.
On iPhones released after the iPhone X there is a sensor on the charging port flex that communicates with the CPU. If this sensor is damaged or missing (as it may be on poor quality 3rd party parts), the device will reboot itself every 2 minutes and 50 seconds. Since you replaced the lightning port here I suspect this is the issue. To verify this issue you can check the panic logs (search "Analytics" in settings, look for a file called "panic-full-xxx.ips" under Analytics Data.
See [post|651841|this question|new_window=true] for more information (different model, but same issue).