Wireless charging packs are convenient but charge slower, as they provide less power. To ensure your iPhone charges quicker, use a USB cable instead.
Check to see if your USB cable is faulty. It could be frayed, damaged, or have internal issues. If your iPhone is charging slowly, try replacing the cable with a new one.
Your iPhone will receive less power if you charge it from your computer. To charge faster, plug the USB straight into a wall outlet.
Not all power adaptors provide the same power. For best results, use either the power adaptor that came with the phone or reputable models from a company like Anker, which also makes fast-charge adaptors.
If you're using your phone while it charges, you'll drain the battery. To charge your phone faster, stop using it and let it charge up. For the fastest charging, turn the phone off completely.
Your connection port could be filled with debris or dirt. Have a look inside and carefully clean it with a toothpick or compressed air.