If your iPhone is not charging when plugged in, the most common reasons and solutions are as follows:

1. Faulty Charging Cable or Adapter: Your charging cable is most likely the issue if your phone isn't charging. Check for signs of wear like fraying or exposed wires. Try using a different Apple-certified charging cable and adapter to see if that fixes the problem.
2. Dirty or Blocked Charging Port: Dust, lint, or debris inside the charging port can block the connection between the charger and your iPhone. Inspect the port with a flashlight and gently clean it out with a toothpick or soft brush without damaging the pins.
3. Faulty Power Source: Sometimes the outlet or USB port you're using may be defective. Try charging your iPhone from a different power outlet, USB port, or power bank.
4. Software Issues: Software glitches or outdated iOS versions can cause charging problems. Restart your iPhone or perform a force restart. Also, ensure your iPhone is updated to the latest iOS version.
5. Battery Health: If your iPhone is older, the battery may be degraded and not hold a charge properly.
6. Unauthorized or Damaged Accessories: Use only Apple-certified (MFi) charging cables and adapters. Non-certified or cheap chargers might not work correctly and can damage your iPhone.
7. Remove Phone Case: Sometimes cases can obstruct the charging port connection, so try charging without the case.

If basic steps don't work, you might consider professional evaluation, especially if there's liquid damage or physical damage to the phone. Quick steps to try:

• Use a different wall outlet, charging cable, and adapter.
• Clean the charging port gently.
• Restart or force restart your iPhone.
• Remove any phone case.
• Update to the latest iOS version.

These are the common reasons and simple fixes for an iPhone not charging when plugged in. If problems persist, it could be a hardware issue needing professional repair.