Have you checked it for fluff? I've found that after a few months of the phone going in and out of my pocket, I just need to scrape out all the dust that's accumulated in there otherwise the lightning connecter gets a bit iffy.
i have, nothing comes out and shining a light in doesn’t show anything obvious in the way, however the cable doesn’t seem to sit snugly in the port, it has a wobble left and right.