Hello blove89,
Being able to retrieve your activity data is important and you've come to a great place for help! To confirm, have you signed back in to your Apple ID on the iPhone? If not, you'll want to sign back in via Settings > [Sign in to your iPhone]. Once signed in, any content synced to iCloud would return to your iPhone and Apple Watch. You'll also want to verify if the activity is shown correctly in the Fitness app on the companion iPhone. You can also find great information about the Activity app on your Apple Watch and the Health apps via the following links.
Use the Activity app on your Apple Watch
Use the Health app on your iPhone or iPod touch
If the activity data doesn't show in the Fitness app on the companion iPhone after those steps, you'll want to reach out to Apple next. You can find their contact details via the following link.
Contact - Official Apple Support
Take care!