Sander van der Zwan, Maarten Smith
The theory specifically focuses on the deep description of human experience and action from a first-person perspective. Key to this is the notion that things “are not neutral ‘intermediaries’ between human and world, but mediators; they actively mediate this relation”. “They carry morality since they help to shape how human beings act.”.
The philosophy of postphenomenology gives you abstract handles to gain a deeper insight into how a design affects our everyday lives; how they shape what our world is and who we are? How do they shape how we interpret the world? What do they enable us to do and constrain us from doing and how do they affect us ethically? These handles help a lot in understanding and designing the transformational qualities of your design.

Rosenberger, R. and Verbeek, P. -P. (2015). Postphenomenological investigations. Lanham, MD: Lexington Books.