DUCT TAPE SOLUTION: Cut a square of duct tape, around 2" in length. Attach to the back bottom of the cell phone (or side, if that is the location of your port). The sticky part will be face up. Insert your loose charger cord, laying it down on the sticky tape. The sticky duct tape will hold it securely. When complete, fold the duct tape for later use. I leave my tape on the phone. Works great in the car, too. Use any kind of tape - electrical, decorative, etc. An adhesive label would work too, even an address label.
Others have posted that lint accumulates in the port. Having the tape in place == as I now have -- covers and protects the port.