Mark W offers some solid tips.
I just replaced my 2016 SE because it was getting very finicky with Lightning cables and syncing/charging. Eventually only one cable in the house would work and only if the Lightning cable was plugged in a certain way (Lightning doesn’t have a good side or bad side but this phone insisted on it). The port was clean and the cables were good and worked with other devices (I tried maybe four of them).
Something similar happened to a relative’s iPad, too. The receptacle for the Lightning cable just wears out or gets misshapen due to stress on the cable or dropping or other damage. Unfortunately, this problem – assuming it’s your problem – is beyond economic repair.