In Safari, bookmarks are automatically synced across all devices that are signed in with the same Apple ID and have iCloud Safari sync enabled.
This means if you create a bookmark on your Mac, iPad, or even your Apple Vision Pro (hello, future!), that bookmark will quietly tiptoe over and appear on your iPhone as well. So, if you’re seeing a bookmark on your iPhone that you don't recall adding, it may have been created on one of your other devices.
Additionally, if you recently imported bookmarks from another browser — such as Chrome, Firefox, or the relic known as Internet Explorer — during setup or through a manual import, those bookmarks will also show up in Safari on your iPhone. Imported bookmarks are treated like any other and get swept into the iCloud syncing process.
If you're finding unexpected bookmarks, it's a good idea to check your other devices and your import history. It’s less “ghost in the machine” and more “you from another screen.”