Note the lack of a bezel and the slightly larger screen area:
So does this part belong to the next iPhone? Maybe, but there's also a good chance that we're looking at a part intended for some Chinese knockoff.
The rumor about the larger iPhone has been circulating for at least a year, and at this point even I think Apple is working on one. But as I have always said, you can't believe Apple product rumors until the components, blueprints, or some other physical evidence leaks. Given that this is just the first leak I think that it would be best to wait for more leaks before forming an opinion.