Safari is the default web browser on all Apple devices, including iPhone. It is updated regularly just like other default apps on Apple devices. On each Safari update, Apple brings new changes be it features or interface. On iOS version 15, Apple made a minor change on the interface where the location of address was moved to the bottom from previously on the just like other web browsers. If you don’t feel comfortable with this change, you can revert the location of the address bar back to top.
To move the location of the address bar of Safari on iPhone, first, open Settings.

On the Settings screen, scroll down and find Safari and tab on it.

Next, scroll down to the TABS section and select the Single Tab option (the right one).

That’s it. The address bar location of Safari on your iPhone is now back to top. From this settings screen of Safari, you can also make other settings if you want to.
If you are curious about the version of Safari on your iPhone, you can open Settings and tab General. Next, tab Software Update. You will see the version of iOS on your iPhone. The version of iOS and Safari on iPhone are the same (iOS 15.5 = Safari 15.5).