Apple Watch

I understand that, since at that point the watch is not really the phone, but an extension of the phone. I just provided that extra information if the OP was referring to a Cellular watch, as some people believe the number is different, since most carriers assign an accounting number to the watch, which looks like a phone number. Calling that number will not do anything, it is only for account purposes so they can bill that extra per month for a cellular watch.

Sorry if you thought I was doubting what you provided.

It usually is the same number you use for your iPhone.

It is the same as the iPhone that it is paired to and cloned from if it is a GPS+Cellular watch.

It was the same as my iPhone even with the original watch which was not GPS or Cellular.