https://techcrunch.com/2019/09/10/why-does-the-new-iphone-11-pro-have-3-cameras/

On the back of the iPhone 11 Pro can be found three cameras. Why? Because the more light you collect, the better your picture can be. And we pretty much reached the limit of what one camera can do a little while back. Two, three, even a dozen cameras can be put to work creating a single photo — the only limitation is the code that makes them work.

Earlier in today’s announcements, Apple showed the base-level iPhone 11 with two cameras, but it ditched the telephoto for an ultrawide lens. But the iPhone Pro has the original wide, plus ultrawide and telephoto, its optical options covering an approximate 35mm equivalents of 13mm to 52mm, and 26mm.