I had the same problem. The problem is caused by cache and directory issues with the startup disk. BOOTING IN SAFE MODE SOLVED IT. Boot in safe mode (hold down shift key immediately you power the macbook, keep holding it until you see the login screen). To confirm that you are in safe mode (safe mode should be written in red at the top right corner of the login screen). Login, plug in your iphone and the problem is solved. To confirm that the problem is solved, leave safe mode by just restarting the macbook normally (without holding shift). Sorry for the late response. THIS IS A 100% FIX
"This post is pretty old but I was about to buy the USB charge doctor to check mine but a coworker suggested I try resetting the SMC on my mac and that fixed it in less than 5 mins. So anyone that’s still dealing with this should try that before buying something to check their USB ports. Here are instructions.