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: https://dictionary.cambridge.org/dictionary/english/smart 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”.

I think the smartphone got it's name from the fact that it can do a lot of different things all in one device, i.e. it's multifunctional. Before smartphones, mobile phones could only do a few things. Multifunctional phones are therefore 'smart', in the same way that a human that can do lots of things really well is also called smart.

and smart for a person can mean intelligent, it can mean they are well dressed or it can mean they are street-smart rather than traditionally intelligent

In a way, I think they are called smart phones because they’re “smart.” They have capabilities beyond that of a regular phone, and I think that’s how they got the name