Navigating by voice commands not possible?

Hello,

I tried using the app on my smartphone to route me for the first time today. As I didn't have a mobile phone holder on my bike, I had to put my mobile phone in my jersey pocket. Unfortunately, the voice commands for routing then failed to materialise because the GPS connection was apparently interrupted when the display was off. Or is there a setting that I can use to ensure that I receive voice commands even when the mobile phone display is off?

Thank you for your feedback. 

Best regards, Uwe