How to spy on a cell phone without having it?

How to spy on a cell phone without having it?
Spyware for Android and iOS allows to spy on a cell phone without having it. However, it’s crucial to understand that the installation on Android target devices requires one-time physical access.
To spy on iOS devices, there’s no need for physical access. However, when setting up a spy app on an iPhone, it’s necessary to know the iCloud credentials and make sure iCloud backup is enabled.