My phone isn't charging

take it to a phone repair store or do the repair your self

You can purchase a new motherboard and install it or try doing some micro soldering and replace just micro USB port. I would go with placing the motherboard but, its up to you. I wish good luck with your fix!!! :)

Quick and free of costs:

This problem is caused by the build up of dust in the USB socket. Consequently the plug can no longer be inserted properly.

In order to avoid short circuiting during the procedure remove the battery. Take a needle and pick out all dust and dirt form the USB socket. Keep going, you'll be amazed by how much will come out.

Once cleaning is done you can reinstall the battery.

Plug will go in like never before ;-)