Choose a workout. Strap phone to arm, or leg. The same tracking magic is now on iPhone. Use iPhone's motion sensors to track reps and track advanced stats like Velocity, Power, Tempo, Speed, Consistencies.
1. The flow on phone is different from the watch. There is no auto advance, you must tap to forward after each rest and set.
2. It works independently from watch. You can strap phone to leg to track leg movement, but you must start a separate workout on phone. It is treated as a different workout from a workout on watch.