You need to have SIM card inserted and flight mode switched off.
- On the start screen, tap Phone > ... > settings.
- Under Show my Caller ID to, open a list and select no one.
If your phone does not have this calling option under phone settings
- Caller ID is a feature set by your mobile operator. If your mobile operator does not support and has removed this feature, search online your mobile operator support page if they have an alternative option to hide your phone number when you are making a call.