Comment by est31

The other component is that once they have the phone number, they can do anything with it they want, unless you leave the network. E.g. facebook once did the same, they required phone numbers "for two factor authentication". They promised to not use the numbers for anything else. A few years later they started sending SMS spam to users about what their friends did on facebook, and now facebook users can enter the number and the associated accounts show up... even though the number was supposed to be only for two factor auth. Your only choice as individual user is to leave the platform.