You still haven't stated your Roku model # or firmware version: Settings/System/About
It's not clear what you are trying to do: Is there some reason you just dont use the Cast function (icon) in YT and cast the YT content via DIAL to your Roku? Are you trying to play the video portion of the YT content on your phone and the audio portion on your TV/AVR/HTS (via your Roku model # unknown) hence why you are using BT instead of Casting?
It's also not clear what you mean by "BT disappeared from our settings" - if your model is BT-enabled (480x), you can pair a new BT device: Settings/Remotes & devices/Pair Bluetooth device and after pairing the device will appear in Settings/Remotes & devices/Bluetooth devices and a BT "app" will appear in your app list- are you saying neither of these menu items/app exists for you, but once did?
Again, you need to provide your model # and firmware version and perhaps answer the questions asked in order to be helped.