Hi @Anonymous User
I don't think this is possible since nowtv blocked mobile smartphones a while back to prevent them playing back on a TV or Monitor remotely by means of an HDMI cable, USB cable or Lighting cable.
Perhaps somebody who owns or use a Samsung DEX Dock on here can confirm either way when using nowtv ?
If no response from anybody on here, then maybe if you have any spare free trials left on your account you could double check if the Samsung DEX Dock works.
Should you take out a free nowtv trial make sure that you cancel it fully before the trial ends.
If you wish to use your Samsung Android phone through your TV with NowTV, then possibly look at a Chromecast device or NowTV stick (assuming you have a spare HDMI port available on your television set) ?
On my Note 9 doesn't work, it says you can't use Now TV while using hdmi cable, it's really stupid since the account allow you to use on a computer and stream using hdmi cable, what's the difference between a computer and a smarpthone for then???
BTW this is the worse streaming app that I have used in my life, the OS X (Mac) version it's broken, if you change the audio device while streaming, the app can't change the audio output, you have to close Now TV app, and open again so it can use the new audio output device.