How do I find my phone number for the Apple Watch

That number would be for billing purposes only. It is not a number anyone can call.

Your Apple Watch does have a separate telephone number but its ID is your iphone’s number. To get the actual telephone number of your watch, log into your account with your cellular provider and go to your device list and select your watch. The actual watch’s number will be displayed.

If you have activated the cellular functions on your Apple Watch with cellular, it is sharing the phone number of your iPhone.

You bring back my AT&T engineering days. It's called a BTN. The TLA* should be easy to suss out 🙂

*Three Letter Acronym

I don't recall ever using that. iPads certainly had them during my Verizon days. But, it makes sense.