You do, however, need to connect to your iPhone when logging a finished workout. After selecting Finish Workout on the Apple Watch, you will be prompted to open Fitbod on your iPhone. From there, you can log your finished workout.
Please keep in mind that manually adding sets, replacing exercises, adding exercises, view exercise demonstration videos, etc. will require your iPhone.
The developer kit for WatchOS is very limited so we aren't looking to add additional features to the watch just yet. Improving the Apple Watch and iPhone experience is on our roadmap when our development team feels the watch platform becomes more stable.