It doesn't charge, it doesn't increase,

@noenoe38850 first check your charger. Make sure it has proper output. Then check your charging cable. Check to make sure connectors are not bend etc. After that, check the charging port. Clean it of any debris etc, use a few puffs of air to clean it out. If none of this works, get a USB ammeter and see if your phone draws any amperage from the charger. If it does not it is possible that this is a charging port issue or a bad battery.

Sine iFixit does not yet have a specific guide for that, use something like this video and this on for the charging board. Batteries and charging board are readily available at many online stores.

While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has the same issues with their phone. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.

Repair is War on Entropy!