Yes, the metro tile, modern style, start screen (whatever you want to call it) looks like the tiles on the windows phone and there is some integration between apps.
I must confess that I have little experience with the windows phone. I have used one in a store so correct me if I am wrong.
Is there a desktop on the windows phone? It seems to me that it would be quite awkward to use it. Can I install Office 2010 on a windows phone? I doubt it.
So aside from the start screen, how do you justify your claim that Windows 8 is a "phone OS"?