Assuming that there's some functionality by which if you know someone's phone number, you can identify them in some UI, how would you salt this? Do you salt al

Assuming that there's some functionality by which if you know someone's phone number, you can identify them in some UI, how would you salt this? Do you salt all the phone numbers with the same salt? Do you send out the salt and expect phones to respond with the salted hashes (in which case, how does this achieve anything?). Do you salt based on geographic location? (Again...) Do you make every phone use the same salt and try to hide it?