They've been a hit with kids (and adults alike) since 1962 mate. That far outlives any phase, it's more like....I mean recently a lot of younger people have gotten into the Beatles. So much so that retail stores are selling t-shirts and things. I just mean it's become a big phase with the younger generations in the last few years.
An insitution?you could argue that they are, have been and still are a phase since they began. But, that's not really a phase it's something else that I don't have the right word for.