Wait, is that what they are actually called?? 
Ok, so here is a screen: www.diablowiki.net/images/thumb/0/01/Grift-selector-ptr230.jpg/450px-Grift-selector-ptr230.jpg
So there is a heading at the top saying “Nephalem rifts”. Then a sub-heading “Select a rift type”, which has the two options “nephalem” and “greater”.
I can see how someone would argue that it’s “greater nephalem rift”, carrying the “nephalem” from the top heading, saying they are all nephalem rifts. But by that argument, the other kind would be “nephalem nephalem rift”, which is silly!