How can I withhold my number in outgoing calls?
You have to set this option at your provider.
As far as I know, there’s no option in the settings of the Fairphone to arrange this.
It can be set at SIM level, but I’m not sure where the toggle is in Android 5 (could be the same place, just can’t check). In older versions of Android it can be accessed from the dialer app, via the (hardware) menu key and then settings > Voice Call > Additional Settings > [SIM] > Caller ID.
On the FP2: In the Phone app, open the menue in the upper right corner and then go to
Settings–>Call settings --> SUBS Settings–>GSM call settings–>Additional settings–>Caller ID
Thanks Irina, this worked.