Do a google search for HDMI Phone to TV Cable and your phone model. I found one for mine and bought it on Amazon, it works great! (in the house, haven't tried it out in the camper yet I admit, but I plan to!)
I know there is some kind of HDMI for iPhone because Technomadia uses it.
If you can connect the phone to TV via HDMI, then you'd use the TV's connection to the stereo using AV input? Or whatever stereo input you use to watch Antenna or Cable TV? I do notice on the back of our TV in our camper there are stereo cords that are from the "audio out" going presumably to the stereo "audio in".
Haha, I'll have to go try that out now that I think about it. I too would like to stream Netflix from the phone to the TV so we can use the "Binge On" features of our data plan.