Glasses are designed to be worn on the face and put into a case when not in use.
A phone is designed to be used to make calls, text and many other features these days, and stored about ones person when not in use, usually in a pocket, sometimes even a trouser pocket. As many models of phone have managed to survive being in peoples pockets for 20 something years, then yes this is a design flaw. (which could have been foreseen a while ago with other manufacturers
http://www.xperiablog.net/2014/01/13...by-some-users/)