Use your phone’s built-in caller ID blocking feature
Android: Settings → Calls (or Phone) → Additional settings → Caller ID → Hide number
iPhone: Settings → Phone → Show My Caller ID → Off
Use a per-call block code
iPhone/Android (US/Canada): Dial *67 followed by the number you’re calling
UK: Dial 141 followed by the number
Australia: Dial 1831 followed by the number
Ireland: Dial 142 followed by the number
Check local requirements for other countries/regions
If you use a carrier/VoIP app, enable “Hide Caller ID” in the app’s settings
If blocking is not available, contact your carrier for caller ID blocking options