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Could be something touching behind it or it could be in the cord for the phone charger.
Try something else in there and see if you can figure out if it's the charger or the outlet.
have you looked inside of the cylinder to see if a dime or a penny fell in it? If that is clear then you can generally take apart the male connector as there is a fuse in there. Take it apart and make sure there is not any wires shorting inside.