As far as I know, no built-in feature on the iPhone automatically deletes call logs after they are made. However, there are some workarounds that you can try:
1. Use a third-party app: There are apps available on the App Store that can automatically delete call logs after a certain period of time. One such app is "Call Log Pro" which allows you to set a time for the call logs to be deleted.
2. Reset network settings: Resetting network settings on your iPhone will erase all your saved Wi-Fi networks and passwords, cellular settings, and VPN settings. It may also delete your call logs in the process. Go to Settings > General > Reset > Reset Network Settings to reset network settings.
3. Manually delete call logs: You can manually delete call logs by opening the Phone app, tapping on the Recents tab, and swiping left on the call log you want to delete. Then tap Delete.
Keep in mind that deleting call logs can have implications for your privacy and security. If you're concerned about privacy, you may want to use a third-party app that securely deletes call logs rather than relying on the iPhone's built-in functionality.