The Cocoa (Touch) Document here say:
Cocoa Touch, which includes Foundation and UIKit frameworks, is used for developing applications that run on iOS.
But the Core Services Layer Document here say:
The Core Services layer contains fundamental system services for apps. Key among these services are the Core Foundation and Foundation frameworks, which define the basic types that all apps use. This layer also contains individual technologies to support features such as location, iCloud, social media, and networking."
So which layer of Foundation.framework is belong to.
Cocoa (Touch) is the all-encompassing umbrella for the layer stack. The Cocoa (Touch) Application Layer is a specific layer within that stack and is sometimes referred to as simply the Application layer.
The Core Foundation framework and the Foundation framework are both part of the Core Services layer.
As you mentioned, here is the Apple Documentation on the subject.