possible, you should contact your wireless service provider and get a replacement phone with the same phone number. Steam will be able to send SMS messages to your replacement phone, and you will be able to recover your account as described below.
If you no longer have access to your phone and you don't remember your recovery code, go to the Steam Support page and create a support ticket. Submit a question with "[Steam Guard]" in its Subject, categorized as "Account Questions" and then "Steam Guard/Email Verification." If you don’t have access to the email address that is currently associated with your Steam Account please provide proof of purchase within your ticket.