Apple wants to make fitness even broader in its ecosystem and more or less casually dropped during the WWDC keynote that the fitness app will be active on all iPhones. So far, the app only appears if you own an Apple Watch.
So now everyone can use the app and if no watch is available, only the movement ring will be active. The iPhone’s sensors are then used to determine steps, distance traveled and exercise calories. Workouts from other apps are also imported. Fitness+ still requires an Apple Watch.