My I iPhone use to reset sometimes

Your iPhone restarting on its own is likely due to a damaged sensor. There are many parts the phone checks for every few minutes and if they do not respond the phone restarts in an attempt to get the sensor to respond. Most commonly on your model it is a bad barometric sensor on the charging port flex cable. There are other possibilities as well. You can look for a panic log in the analytics section of the settings. If as panic log is present the info there can help you to narrow down the issue.