Open the Phone app
Tap the three dots menu
Tap Settings
Tap Supplementary services
Tap Show your caller ID
Select Hide number
If that option is not available, open the Phone app
Tap the three dots menu
Tap Settings
Tap More settings
Tap Caller ID
Select Hide number
To hide your number for one call, dial #31# before the phone number
To make your number private through your carrier, contact your mobile network provider