Not even the NSA has a database of famous person phone numbers. Most of the rich and famous don't have phone numbers, or even mailing addresses. They have companies that in turn manage their devices and properties, usually run through a "family office" of attorneys and accountants. So the NSA will have a list of numbers associated with their production company or family law firm, which would require further human investigation to determine which was actually in a person's pocket day to day.
Politicians have started adopting such structures too. House Speaker Mike Johnson famously has no bank account. He does, just not under his name. It would be managed by his family office.
I worked for telcos, and the rich & famous & royalty typically had their accounts restricted from access by regular CSRs. I know there were restrictions built into the internal systems, though it didn't apply to my role.
Now the elite use Telegram groups, Signal, and rotate SIM cards. Everybody should be doing life this way, so the telcos become dumb data pipes.
I don't think this is close to universal among rich and famous, although no doubt you are correct about some. For one thing there is a principal agent problem in giving this kind of personal service company control over all your comms. Big impersonal companies can be more relied on to treat everyone the same. Many famous people will just sign up under a pseudonym.
Family offices are also an artifact of generational wealth. Plenty of famous people aren't rich enough for something that heavily staffed. Also newly wealthy will often want to be able to deal with existing friends and family on the same basis as before.
Indirectly, I've been able to observe some of the habits of someone with stratospheric levels of wealth. They had a phone number, but changed it frequently.
In some respects, uber wealthy and street/cyber savvy criminals act same: use intermediaries, use cash, use trusts incorporated in states/places, where it is hard to trace beneficiaries, burner phones bought with cash, by intermediaries, frequent change of phones, no trace of their names on data brokers, consultants who help get rid of any trace in data brokers, etc.
Politicians have started adopting such structures too. House Speaker Mike Johnson famously has no bank account. He does, just not under his name. It would be managed by his family office.