There is no single button or feature to close all open apps at once on an iPhone, as Apple's design intentionally prevents this to optimize battery life and performance. Instead, users must manually close apps one by one or use a multi-touch gesture to close up to five apps simultaneously.

To close apps manually, access the App Switcher (swipe up from the bottom and pause on Face ID models, or double-click the Home button on older models), then swipe up on each app preview. For a faster alternative, you can use multiple fingers to swipe up on several app previews at the same time, though this method depends on having enough screen space and may require two hands.

Important Note: Apple does not recommend closing apps unless they are frozen or unresponsive, as the iOS operating system automatically suspends background apps to save resources. Constantly closing apps can actually consume more battery than leaving them suspended, as the system must reload them from scratch when reopened.