All I can find is from this article here:
https://help.netflix.com/en/node/23927
Resolution
iPhone and iPod touch models support streaming up to 720p in iOS 7.0 and later, and 480p in iOS 6.0 and earlier. All iPhone Plus models beginning with the iPhone 6 Plus support streaming up to 1080p. iPhone X, XS, and XS Max support streaming up to 1080p, while the iPhone XR supports streaming up to 720p. iPads support streaming up to 720p in iOS 7.0 or later, and 480p in iOS 6.0 and earlier. iPads with Retina displays support streaming up to 1080p.
This doesn’t specify which plan you need to have in order to get those resolutions though. But hopefully this helps a little bit.