Okay, I had been facing the same issue since the past couple of months with my more than 2 yrs old 6s. Today, just moments back & out of curiosity & boredom combined, I took a tooth pick & started scraping the inside of the phone’s charging port. To my surprise, a shitload of debris started dropping out. After about some ten minutes of ‘not so careful’ scraping, the port looked clean. Post which I checked for charging, & the “lose port” problem disappeared. Contrary to my belief as per which, more the debris inside the port, tighter should the connection with the cable upon plugging in become, cleaning gave that rock solid port-cable grip back. Apparently, the base of the port starts getting deposited with debris, & hence, the cable does not fully go in, which results in a fragile connection. Do give it a shot!