Do I need to have my iPhone with me or nearby?
SmartGym for Apple Watch is a completely independent app. There is no need to have your iPhone with you or even nearby. You can leave it in the bag or at home. All changes you do on your Apple Watch will be automatically synced to your account.
For users in the Local Features plan, just make sure your initial data is synced first. Then, all changes made on your Apple Watch will be automatically synced once both devices are near each other.
Tap here to learn how to use the Apple Watch app independently.