You can NOT overcharge a device with a Li-Ion battery or any other lithium based battery(thus the reason you can leave a notebook plugged in all the time if you want) since it would blow the battery up. The chargers are designed to stop when they get full.
I would contact your provider of phone maker to see if you are missing something or just have the misfortune of developing a defect.
You also did not tell people what phone you had.