Just because you opt out of letting Facebook (or Linkedin) see your contacts, does not mean your contacts have done the same thing.

e.g. If you are someone@example.org, and others have someone@example.org in their address book and they let Facebook see it, they've got you already.

For this reason I use a dedicated email address for each social media account.

Also, while I'd normally recommend 2-factor authentication, giving these guys your phone number is a really bad idea if you value your privacy. Try to limit it to firstname lastname and one throwaway email if at all possible. If you're really paranoid, you can get a VOIP gateway that supports SMS for fairly cheap, certainly for cheaper than buying a burner phone.