Apple watch series 4 stop recieving phone calls while phone is off.

Should we assume that you have the cellular model and that you have activated it on your cellular plan?

Why are you turning your phone off at all? Do you see the same behavior if the phone is on, but in Airplane mode?

If your watch is the GPS version without cellular this is working as designed, because it makes all its external communication via the paired iPhone. If you have the LTE version of Apple Watch please start with the easy stuff by checking the cellular connection when the iPhone is powered off. Swipe up for control center and check the connection status indicator top left of the screen. If it shows a cellular connection has been made you could also try making an outward call from the watch, to see if the blockage is both directions or only one way.

Let us know what you find, you are our remote eyes.

Please back up and rephrase your last post. The only thing that made sense was "yes I have cellular"... I read the rest of it 3 times and gave up trying to figure out what you were saying.