Yesterday, Microsoft pushed an update to its Your Phone app for production versions of Windows 10, activating the feature within the app. Today, that update has been removed, meaning that you can't get it on Windows 10 version 1803 anymore; however, if you already have it, it should still work.
According to the team's Vishnu Nath, there are some "quality and disclosure issues" for now, which will eventually be fixed. In other words, this will still arrive on Windows 10 version 1803 at some point.
Even though it was on production versions of Windows 10, Your Phone was still far from complete. For one thing, it only works with Android, even though the iOS experience will be limited when complete. The app also only allowed users to view their most recent 25 photos from their gallery.
Aside from helping you to integrate your phone's photo gallery with your PC, you'll also be able to make calls, and send and receive SMS messages. Again, none of these features are live yet, even for Windows Insiders.
If you want Your Phone right now though, you're going to have to be a Windows Insider. It will definitely work in the Fast and Skip Ahead rings, and it should work in Slow as well, even though Microsoft hasn't specified the Slow ring.