Hi marlo254,
These verification codes use SMS text messaging to contact your iPhone as mentioned in Automatically fill in one-time verification codes on iPhone – Apple Support
If you are not getting these codes make sure you can receive SMS texts with the steps in the resource linked to your post, If you can't send or receive messages on your iPhone or iPad
We also recommend restarting your device and keeping it updated as those steps assure you have cleared out any minor software issues and are running the most current version.
Restart your iPhone - Apple Support
Update your iPhone or iPad - Apple Support
If you still have questions, reach out to your wireless carrier as SMS texts are a carrier supported function.
Cheers!