In case it’s helpful to anyone else out there, I had some trouble connecting my phone to a Wear watch.
The gist is, if you pair your phone with the watch from the Bluetooth settings screen instead of the Wear app, the watch will happily connect and try to update/sync, but your phone will never figure out that they’re connected. The first walk-through I read indicated this was how you were supposed to do it, but current versions don’t support this flow. Either this was inaccurate, or an update broke compatibility.
So to save yourself the grief I went through of having to FACTORY RESET YOUR WATCH SO YOU CAN RE-PAIR IT (!!!), make sure you enable Bluetooth in the phone settings, and you can see the watch, but don’t pair with it from there! Do it from the Wear app.
Full, accurate (if spartan) instructions can be found from Google: https://support.google.com/androidwear/answer/6056630?hl=en