The green stuff that can sometimes accumulate in the charging port of your cellular device is a form of corrosion -- due to extended use of your phone. You will see this a lot in older phones that have been in use for a year or more. The good news is that there is a quick way to clean out this green stuff and ensure that the charging port is clean and viable.
Power off your phone and unplug the charger cable if it is attached.
Turn the phone over and remove the battery cover from the rear of the unit. Remove the battery.
Dip the bristles of your toothbrush in rubbing alcohol to the point that the bristles are moist but not dripping wet.
Use the toothbrush to clean the charging port of the phone. Use even strokes and moderate pressure. Continue until the green residue is removed from the phone and allow the port to dry.