Ghost touching while on a charger is usually caused by using a charger other than the 1 that was originally supplied with the phone. I found that to be the case in almost every example.
As for ghost touching while not connected to a charger, that can be attributed to things such as liquid, oils or dirt that may make it down along the edge of the glass display.
Other than that you could have an app that's causing the problem, or it could be a defective display.
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