you are right about a Watch that is set up through Family Sharing being able to get calls to its otherwise hidden/not used cell number.
as has been mentioned, i dont think you can do what you want (receive calls on the hidden watch cell number) if it is paired with your own iPhone.
if i understand you correctly, couldn't you be able to do what you want by having your own watch paired with a family member's iPhone through the Family sharing process? that would allow you to receive calls on yr iPhone through your main iPhone number(or turn off the cellular facility if you dont want to receive calls on yr iPhone) as well as receive calls placed to your Watch through a Family Sharing process?
it would take a trusted family member to do that, im sure.
Just to clarify, I got my first Apple Watch a few months ago when my iPhone used a carrier that didn't support watches, so my new watch was set up - by a kind relative - with family sharing, and I was very happy with way the phone access worked. But I then found that dozens of watch apps don't work in "Family Sharing" mode!!
So I decided to switch to a (more expensive) iPhone plan, while foolishly thinking that if I had a "Standalone" cellular watch plan from the new carrier I'd have two independent phone numbers, while also having all apps supported.
Doesn't work that way! (Maybe someday)
So in addition to moaning and groaning, I thought I would come here for advice.
Please take pity on this newbie...
I carry my iPhone with me during the day so there is no issue if calls go to both the phone and watch. When I come home I toss my phone in the corner and just talk to people when I damn please! Only if relatives or friends need to reach me would I want to be bothered. I guess this is what "Do Not Disturb" is for - but I can't find any detailed doc on this.
Is there the same flexibility on the watch for exceptions to DND - "Emergency Bypass" or "Allow Calls From"? How do folks deal with this problem (if this is a problem for anyone else).
Thanks to everyone for your help!