what or where is the button bar on an iphone?

The iPhone XR, like many other iPhones, does not have a physical "button bar" in the traditional sense. It features a nearly full-screen design with a gesture-based navigation system rather than physical buttons.

Here's how you can interact with the screen:

1. Home Gesture: To return to the home screen, swipe up from the bottom of the screen. This gesture takes the place of the physical home button found on older iPhones.
2. Control Center: Swipe down from the upper-right corner of the screen to access Control Center.
3. Notification Center: Swipe down from the upper-left corner of the screen to access the Notification Center.
4. App Switcher: To access the app switcher or switch between recent apps, swipe up from the bottom and pause in the middle of the screen.
5. Siri: You can activate Siri by holding down the side button on the right side of the phone.

If you are referring to a specific app or function that you believe is called the "button bar," please provide more context so that I can give you a more accurate answer. It's possible that the term "button bar" could be used in the context of a particular app or feature, and the location or appearance of such a bar might vary between apps.