@tyagimeenakshii I am a bit confused by your question.
What do you exactly mean with "screens" and how the screen size is related to the complexity of the experience?
I think, in a nutshell, that there's one UX basically based on humans. What can be complex and/or easy is the relationship between humans and products.
For example a screen providing a login. The UX is always the same, give access to the product/service. What should be evaluated is the way how we are delivering such feature (one field, finger prints authentification, token etc) and how much our users are happy with it.