Is my phone eligible for trade-in if it only has a bad charging port

Any trade in device will be checked to see that everything works.

Apple would only repair it as a full out of warranty replacement.

Apple will accept phones that are not working depending on the model and what is wrong with it but it seriously impacts the price they offer.

Sure. However a charging port is not something that Apple fixes. That would mean replacing the entire board assembly with the port, charging circuits, etc. Even if it’s not a complete replacement cost, that’s got to cost more than an iPhone 6 trade-in value.

If you are trading in your iPhone whether the iPhone store repairs that or not is irrelevant. Apple at their refurbishment depots does indeed to part-by-part inspection and replacement. But in this case the trade-in (in the USA) goes to Brightstar, not Apple, and they do various levels of refurbishment. And the OP is trading in an iPhone 7.

Hello,

The phone will be evaluated as part of the trade-in process:

Turn the device you have into the one you want

Good luck.