You can add and verify your phone number on your Profile page.
Tips for troubleshooting if you're not receiving the verification SMS:
Double check and make sure you have entered the correct phone number.
Some phone operators block incoming text messages, try contacting your phone operator.
The carrier may have an error, and the text message may not have been sent out successfully. Please feel free to contact our support (firstname.lastname@example.org) if you have unsuccessfully tried to verify yourself for five times in 24 hours.