If you’re annoyed by the many open tabs in Safari for iOS, you can close all of them at once using a simple trick.
On Safari “Tabs” listing screen, tap the “Private” button at bottom left to activate private browsing. You will be prompted with options before entering private browsing mode. Select the “Close All” option to remove all open tabs in Safari.
Toolbar and menu bar of Mobile Safari will be black in color when you’re in private browsing mode. To toggle back to normal browsing, repeat the same by tapping on the “Private” button again.