Dial *67 before the number you want to call
On iPhone, go to Settings > Phone > Show My Caller ID > turn off
On Android, open the Phone app > Settings > Calling accounts or Calls > Additional settings > Caller ID > Hide number
Contact your mobile carrier to block your number on all outgoing calls
Use a secondary phone number or calling app that supports caller ID blocking
Check whether the recipient’s carrier or phone settings may still display your number in some cases