I found an on-target definition of good design here in a slideshow on the Bentobox model for understanding technology stacks. They use the Japanese term “Ekiberi” – “content which is arranged in the most efficient, graceful manner. .. Nothing lacking, nothing superfluous, not decorated, but wonderfully designed.”
Good design can be subjective based on the subjectivity of ‘what’s needed’ and what good arrangement is. However, this definition fits the intuition that form should follow function, and that efficiency can make for a better user experience. The best designed products reflect this aesthetic. iPhone surely fits this.