Do I need to print out my voucher before hand or can they just look at my phone?

Phone is enough

I used the mobile tickets on my phone on Saturday. Was not an issue at all!

The voucher on the phone is enough. Enjoy!

It should be enough if they can just check it on your mobile phone, but I'm not 100% sure. It's better to give them a call & to confirm it.

All OK. But there is no audio guide in Russian