To get rid of the circle - assistive touch - on the iPhone screen, you can go to Settings > General > Accessibility > AssistiveTouch and toggle the AssistiveTouch button to the off position. Alternatively, you can triple-click the home button (on older iPhones) or the side button (on newer iPhones) and select AssistiveTouch and then Device and then toggle the AssistiveTouch button to the off position.