The iPhone backup location can be found in the following directory Alternatively, if you have more than one iOS device backed up on your Mac, you can search for a specific backup in iTunes. When you backup your iPhone to your Mac, files are automatically placed in iTunes.
(For me, I recently had issues with both macOS High Sierra 10.13.5 and macOS High Sierra 10.13.6 with my iPhone running the iOS 12 developer beta 3.) In this case, you'll need to be running the latest beta version of macOS, which, for the iOS 12 betas, would be for the macOS Mojave 10.14 beta.
