It may not actually be the cord itself but the jack (on the phone) it is plugging into. Is it loose? Have you checked if for damage, dust, etc.?
If it has anything stuck in it, be careful not to damage anything in the jack when you clean it out.
If it is loose, then you are going to need to get it repaired. If it is under warranty still, I would suggest contacting the manufacturer. If it isn't under warranty, then you are free to have whoever you want repair it.