Previously, Apple had not approved third-party browsers for the App Store; its own Safari browser is preinstalled on the iPhone. Other browsers weren't allowed, citing "duplicating functionality."
The browser apps currently in the App Store all have some kind of quirk that sets them apart from standard browsers, ranging from a slant in design (Edge) to one in privacy (Incognito). They're all built using Safari as a base too. So it's not yet clear whether Apple will open the gates to iPhone versions of completely separate third-party browsers, such as Firefox or Opera.