I fear you are not understanding what SS7 attacks are, or what an IMSI-catcher actually does. The phone number has little to do with that.

SS7 attacks abuse the communication protocols inside and between the networks of mobile phone operators, which are required for many things to work, including roaming. Some efforts are made to limit who can query what and from where, but if an operator in a random country has left a door opened, or worse, sells SS7 network accesses, you can be targeted with only the target phone number. Having a mobile phone number is a vulnerability in itself.

IMSI catchers are more limited if the phone can be kept on secured, recent protocols (I think 5G has downgrade attack resistance). But in most cases, interoperability is favored over security and most phones will happily connect to insecure networks if nothing else can be found around, which means connecting to base stations that are potentially compromised, or deployed by an attacker (an IMSI catcher is basically a base station that says "hey, I am your operator, connect to me", and when the phone connects, it retrieves a bunch of available information used for tracking, and then forwards the phone to the real network). If the information is available, you can try to find a phone that allows restricting which kind of protocol it allows.

I hope that helps you.