Here's how you can block your caller ID on an iPhone:

1. Open the Settings app on your iPhone.
2. Scroll down and tap on Phone.
3. Tap on Show My Caller ID.
4. Toggle off the switch next to Show My Caller ID.

That's it! Now your caller ID will be blocked for all outgoing calls. If you want to block caller ID for one call only, dial *67 before the number you want to call.

I hope that helps! Let me know if you have any other questions.