The bottom module contains the USB C port which as mentioned can be damaged and malfunction due to debris and contact tarnishing.
The module can be disassembled and you can better see if it is damaged or dirty etc.
CAVEAT: Disassembling the bottom module will void any warranty
However the actual charging electronics (chips) are on the main board which is not a user replaceable part.
If you have no improvement by cleaning you may find a fairphone angel near you that has a spare bottom module that you can try.