Try rebooting one or the other (or both). There has been a couple of times when it lost the connection and no longer recognized my iPhone. Rebooting fixed it.
Unpair your Apple Watch from your iPhone 6. Then restart you Apple Watch. Once your Apple Watch has finished restarting, pair your watch with your iPhone 6 Plus
Unpair your Apple Watch from your iPhone 6. Then restart you Apple Watch. Once your Apple Watch has finished restarting, pair your watch with your iPhone 6 Plus