Keeping voice routes to premium and shared cost phone numbers open make your Plivo account susceptible to International Revenue Sharing Fraud, also known as Toll-Fraud.
It is advised that you disable outbound calls to premium and shared cost numbers unless your use-case heavily depends on it.
To block calls to Premium and Shared Cost phone numbers globally, navigate to the Voice Fraud Prevention section of your Plivo console.
Mark 'Block Calls To Premium and Shared Cost Phone Number' as 'Enabled' and save click 'Save' to update your preference.
Please note that only Admin users can update this setting.