How can I block my caller ID on an iPhone 8 plus? I cannot find it

If its not in Settings->Phone->Show My Caller ID, then your carrier does not allow that option. You would need to contact them to have them block your caller ID or add the option to your service plan if they offer that option.

Link-> Make a call on iPhone - Apple Support

Go to Settings/Phone and tap Show my caller ID. If you don’t see the setting you will have to call your carrier, and in some countries it is not possible to turn off caller ID.