The answer is deceptively straightforward: If your iPhone screen is locked, the slide-to-answer bar appears, but if your screen is unlocked and open, the decline and answer buttons will show.

Only when your iPhone is unlocked and open will the decline and answer buttons show. When your phone is locked, pressing the sleep button on the side of your phone once will stop your iPhone from ...

With the General tab selected, look for the Button Labels option and click on Text.Scroll down to the bottom, click Save Changes, and you’re done!. Now that’s an interface I can understand.