Here’s my take on this.
The concept of “mirroring” one phone to another is possible, though it often works differently than a simple screen cast. Most solutions designed for this purpose involve installing an application on the source phone. This app then gathers information and syncs it to a dashboard, which you can access from your own device. It’s more of a data-syncing process than a live, real-time video feed of the other screen.
Regarding cross-platform use, like Android to iPhone, that’s where things can get tricky. The level of access and the features available can differ significantly between operating systems. Generally, you’ll find more comprehensive features for Android, while iOS solutions might have more limitations. It’s definitely achievable, but the method and results depend heavily on the tools and phones involved.