My phone is not charging

To fix this, switch your phone off, and remove the battery if you can. Then, put your battery back in, power on your device, and try charging again.

Something inside the USB port, like pocket lint. Your battery might also be in very bad condition.

Is your phone 100% depleted? Sometimes if that's the case leave it on the charger overnight and then see if it started charging again. I've fixed some phones that way with 100% drainage. Another option is the USB connection at the plug is bad and is not really giving any charges even though it says it is. And if all else fails, you might have a bad battery that has overheated and is no longer working properly.

What Albert & Ricky said.

Additionally, make sure you are using a manufacturer recommended charger and a known-working cable for your phone. Also, make sure to plug the charger directly into the wall, not into a power strip or extension cord, as those can sometimes have trouble providing continuous electrical flow to your phone.

If your phone is already on but not charging, doing a Restart can fix the issue. I’ve seen older Samsung phones charge normally after a standard soft restart.