Name a phone number without adding to Contacts? On my iPhone I have a well-curated Contacts list of all of my friends and family.

I also often want to name the phone numbers of more temporary "contacts": one-time business deals, recruiters, friends-of-friends for a single weekend, etc.

I don't really want to add these people to my Contacts forever, but I do want to read their name on Caller ID when/if they call.

Does iOS have any concept of "second-tier" contacts that are saved but not listed as "Contacts" in my address book?

How can I save and name phone numbers but keep them separate from my true Contacts?
You can use "groups" in contacts. I don't know how to create them on the iPhone, but macOS' contacts app allows this. You should check if iCloud allows this. 

https://www.idownloadblog.com/2014/03/01/how-to-create-contact-groups-iphone/

This blog also features an app "Contact Groups". 

 I am not associated with either the linked website or the said app.