Updating to IOS 11.2.5 fix the problem, not sure if netflix update their app, but the last netflix update, I still cannot play Movies from phone to TV via Digital AV, but after updating my IOS 11.2.5, just have a hunch that it will work, due to some security bug patch which I think related to the communication between IPhone and Digital AV... story short, I tried it this weekend, and walahh.. it works... though I feel the video stutters on my 4K(though it output a 1080p), but doesnt have problem on my 32 inch 1080p TV.
and Im referring to downloaded Videos.. tried it on few series, but I guess it will work on movies too..
It also play without also playing the video on my phone.. it works with the phone screen saying "playing movie on tv" or something similar. also the phone screen would automatically turned off. thus preserving the Display life when not needed.
Im using Iphone 6S.. which after IOS 11 update does not work.. then its now working(after the update)