Same experience with signal, but SMS phishing is a very large issue, at least in my country. Maybe your phone number was just never leaked and you're not present in the spammers databases?

email and phone spam would be a bit easier to mitigate if places-we-enter email+phone (websites that want this info) would give us a list of Emails and Phone-numbers it uses to contact us with, and even email-subject prefixes; it is no different than when you meet an old friend and you each, mutually, exchange phones/emails/physical addresses; why are the UX of all the websites so poorly designed that we consumers do not get to see, proactively, the address they intend to talk to us from?