If a number is flagged by you as spam, subsequent calls should go directly to voicemail. A robocall never seems to be missed on Google Voice. Rather they cause

If a number is flagged by you as spam, subsequent calls should go directly to voicemail. A robocall never seems to be missed on Google Voice. Rather they cause a 2 second blank voicemail to be generated. If you have Hangouts integration enabled, you still get a notification for these voicemails.