Switch AirPods from macOS to iOS 11 Using my AirPods with my Mac is easy:


Check the Show volume in menu bar checkbox in System Preferences > Sound.
Ready the AirPods near the Mac.
Click the Volume menu bar icon, and choose your AirPods.


How to regain control of the AirPods in iOS 11 such as on an iPhone? 

The swipe-from-bottom controls have changed radically. So the old iOS 10 approach is gone.

Supposedly, in the new swipe-from-bottom controls, you can use the Apple Music widget to gain control of the AirPods. That's annoying as I am not an Apple Music customer, so the extra taps are out-of-my-way. But anyways, that approach fails. Here is a screenshot of iPhone > Control Center > Apple Music widget > Upper-right corner icon > list of devices, showing iPhone and AppleTV but no AirPods.
With the AirPods near your iPhone (or I put them in my ears and pick up the phone).


Swipe up from the bottom of the screen to show the Control Centre.
Tap on the top right corner of the Music control to show the list of devices.
Tap on "Basil's AirPods".