If you want to position your iPhone for a photo, you can use your Apple Watch to view the iPhone camera image and take the photo. In addition, you can use your Apple Watch to set a shutter timer instead of replying on your iPhone, which will give you time to lower your wrist if you're in the shot.
To function as a remote, your Apple Watch needs to be within Bluetooth range of your iPhone.
Take a photo
Open the Camera Remote app on your Apple Watch.
Position your iPhone to frame the shot using your Apple Watch as a viewfinder.
To zoom, turn the Digital Crown.
To adjust exposure, tap the key area of the shot in the preview on your Apple Watch.
To take the shot, tap the Shutter button.
The photo is captured in Photos on your iPhone, but you can review it on your Apple Watch.