https://www.gamespot.com/articles/fortnite-mobile-features-some-small-changes-from-p/1100-6457455/

Fortnite Battle Royale on mobile is almost exactly the same game as on PC, PS4, and Xbox One. There will even be crossplay between the different platforms. However, there are still a few differences to Fortnite on phones that are meant to assist with playing on a smaller, portable device.

Specifically, the iOS version adds a few visual cues to allow you to play without headphones. Events that otherwise would be conveyed through sound--footsteps or the direction of gunfire, for example--show up in the HUD.