Summary
To close all Safari tabs at once on iPhone and iPad, perform a long press on the tab switcher button and select “Close All Tabs” from the menu that pops up. Confirm the action by tapping “Close All Tabs” again in the pop-up window. Alternatively, single tap on the Tabs icon to bring up the browser window view, and then long press on "Done" to bring up the same "Close All Tabs" interface.
1
2
According to