How do I set communication limits on my son's iPhone?

Hi, I have tried setting Communication Limits on my son’s phone to specific people during Downtime/Screen Time, but when I do this, it essentially blocks everyone instead of leaving the specific contacts I listed available for communication. Since I do want him to be able to reach his father and me in an emergency I have to disable the communication limits. But I do want to curb his texting during downtime hours. What am I missing here? Is there more than one location to make this change?

[Re-Titled by Moderator]