find my iphone with my apple watch

See: Find misplaced devices with Apple Watch - Apple Support

If find my is enabled on your iPhone you should see it in the control Centre on your watch. Swipe up and it’s the icon under the cellular icon. Tap to ping your iPhone..

Tip: if you long press on the icon the iPhone should flash to find it in the dark.

Alternatively, you can add find my complications to watch faces that you can just tap from the watch face. This has more details to view and you can find other Apple devices as well as iPhone.