If you no longer would like to receive the 2-factor text messages, you can install a TOTP like Google Authenticator, DUO, or Microsoft on one of your devices. Now remove the Authy app from your device.
You will no longer receive the text messages until doing a phone reset with Authy. If you continue to receive the text messages, you may want to remove your phone from Coinbase and re-verify. You will then need to follow these steps again.
If you continue to receive unwanted SMS messages, please don't hesitate to contact Coinbase support.