Open your phone app
Go to Settings
Tap Call Settings or Phone Settings
Select Caller ID
Choose Hide Number or Show My Caller ID off
On iPhone, go to Settings > Phone > Show My Caller ID and turn it off
On Android, open the Phone app > Settings > Calls > Additional settings > Caller ID > Hide number
To hide your number for one call, dial *67 before the phone number
Check with your carrier if caller ID blocking is not available on your device