Caller ID isn't working on my iPhone

No Caller ID is the issue only needs to be addressed by the Cellular Service Provider not Phone Manufacturers (Any brand for that matter)

Are you getting a lot of calls from unknown callers (e.g., spammers, telemarketers etc) with “No Caller ID”. You may want to block these calls because you cannot possible identify the number of a caller before answering. These calls may also be labeled as Anonymous, Private, or Blocked.

You are receiving these calls because, in few countries, local authorities mandates that cellular carriers allow people the ability to block their Caller ID, hence No Caller ID. Some ordinary people (VIP) may want to block the display of their telephone numbers intentionally because of some privacy concerns.

There are also more and more telemarketers, spammers using No Caller ID because they do not want to be known.

The good news is that you can block specific callers/numbers/caller IDs using third party apps in the App Store.

This issue only needs to be addressed by the Cellular Service Provider not Phone Manufacturers (Any brand for that matter)

Watch the GIF below till the end.

If you are a VIP they (Cellular Service Provider) will enable it for you.

If you can't turn it on or off because it keeps scrolling try turning off mobile/cell data in Settings.