iPhone 6 won't charge
won't charge above 2-3%
i changed the charging port but no luck
Does it show that its charging(has the lighting bolt)? Have you tried a new battery and charger(both brick and cable)? If it does show a lighting bolt, if you have tried a new battery and also replaced the charging port the only other thing it can be is charging chip set on the motherboard. It will require micro-soldering expertise, if you wants to give it a shot i can give you more info on what chips need replacing.
hope this helps,