If it shows "No Caller ID", this is a serious issue. Get in touch with your Carrier and keep them informed about it.
There is nothing on the iPhone that can be done if you do not get the Phone Number displayed when receiving calls. You can at best --> Avoid unwanted calls on iPhone
When you receive a call that shows "No Caller ID," it means that the caller has blocked their number from being displayed on your caller ID. This is typically done for privacy reasons, but it can also be used by telemarketers or scammers to hide their identity.
If you are concerned that the calls may be from someone you know who is intentionally hiding their number, you may want to reach out to them to see if they can provide more information or contact you from a different number. However, it's important to be cautious when dealing with unknown callers, especially if they are persistent or seem suspicious.