It would appear I can’t use the full size USB socket on the Mavic 2 controller to connect to my iPhone. Is this correct?  
Worked fine on the Mavic Pro.

Yes, you can connect a Lightning cable to the USB port on the bottom of the remote controller. Like when using your Mavic Pro, you'll need to disconnect the cable on the left side of the remote controller before attempting to use the USB port on the bottom.

Ah, I forgot I had to disconnect the micro USB first. All good. Thanks for your help.

Hi there. Sorry for the inconvenience caused. Please use your lightning cable and connect it to the USB port on the bottom part of the RC to your iPhone. For reference, please see the attached image below. Should you have further question, please let us know. Thank you.

This does not only work well for lightning cables (used by a small minority) but also for all USB cables ;-)