Need Help? Call anytime at 1-833-590-0301 for assistance. If you use the Coinbase app , updating your phone number is just as easy. Open the app, log into your account, and go to Settings . In the Security section, you'll find an option to update your phone number. Enter your new number and confirm the update with the code sent to that phone. If you run into any problems during the update, Coinbase support can be reached at 1-833-590-0301 for assistance.

https://www.linode.com/community/questions/39620/how-do-i-change-my-mobile-number-on-coinbase-general-queries