in iOS is it possible to silence call ringing without using Do Not Disturb?
Immediately upon posting this question, I had a flash of insight as to a possible solution.  Turns out it works perfectly!  Here's what I did:


Add a "silent" ringtone to your phone (instructions at https://www.wikihow.tech/Set-a-Silent-Ringtone-on-an-iPhone or just Google "silent ringtone on iOS")
Set this silent tone as your default ringtone under Settings > Sounds
Enable a custom ringtone for all contacts that you actually do want the phone to ring for.


Note that the caller must not have their caller ID blocked for their custom ringtone to work.

Now your phone will only ring on calls from those specific contacts, and nobody else, all without using DND mode or disrupting any other notifications on your device.  Nirvana!