Phone keeps turning off when charging

Carefully, under a good light, check the charging port to see if there is lint or other debris lodged in it. I you see anything, using something non-conductive like a toothpick, work it out.

Also, check to make sure that the outlet you're using isn't connected to a wall switch that can turn it off. Sometimes, only one of the two receptacles is connected to the switch.

have a look at your charger, is it the correct charger for your phone, it might be a thermal response by overheating