@Anonymous User I assume you don't have an HDMI cable coming out if the back of your phone. Did you recently update the firmware? Sounds like Sony might have left a flag suggesting that you are outputting to a big screen, which NOW TV doesn't support.
Hi @Anonymous User,
We are aware of an issue with this and it's currently being investigated. I've passed your details on and you will be contacted by email as soon as it's fixed.
NOW TV Team