Why is my phone not charging

When troubleshooting it's best to start from the easiest things and work your way up. Have you tried a new cable and charger on a different outlet?
If that doesn't help, have you tried to clean out the charging port? They can get lots of lint, dust, and dirt in them over time and it can cause charging issues. The best way to clean a charging port is using thin tweezers to get out any gunk.

Clean your charging port with toothpick be careful then plug your charging if it still not working then get a new charger