I didn't think Donna Murphy seemed tiny at all when she played Phyllis, she looked statuesque next to Victoria Clark too. There's no "problem" in casting Murphy as Phyllis whatsoever, she's brilliant in the role and there was a general feeling that hers was a Tony-worthy performance. However, I'm more excited about the idea of having her back on Broadway.
I love the idea of Sigourney Weaver as Phyllis, though of course I doubt there's a way she would be part of this production if she turned down an offer to do it on Broadway. Jean Smart sounds interesting though there's many actresses I'd rather see (such a shame it didn't work out with Williams or Cattrall).
"Some people can thrive and bloom living life in a living room, that's perfect for some people of one hundred and five. But I at least gotta try, when I think of all the sights that I gotta see, all the places I gotta play, all the things that I gotta be at"