https://www.cnet.com/news/olloclip-gives-iphone-x-users-a-camera-lens-system-of-their-own/

Apple's iPhone X already has a great camera, but if it's your only camera maybe you'd like a little more shooting flexibility. And that's where Olloclip comes in. 

The company, which has been developing iPhone camera lenses since 2011, is back with a new dual-lens Connect X mount designed specifically for the iPhone X. The mount allows you to use add-on lenses with either the front or the rear cameras. You no longer have to flip it around like you did with older models. Instead you just clip on the mount and then swap out the individual lenses with a simple push-button mechanism.