A very common usage of “smart” in British English is what we in America, would probably just call stylish. It’s actually the first definition listed in the Cambridge Dictionary:
As far as the “smart phone” (emphasis on “smart”), I believe it’s a reference to the telephone’s being intelligent — able to “think”. I suppose that in British English, with the emphasis on “phone”, it could conceivably mean “stylish”. Or perhaps that would be “a smart smartphone”.