That's a very misguided title. The only way that could be considered to be true, by their own standards, is if zoom is the most important quality of a smartphone. On all the aspects of photography that actually matter, the P2XL beats it hands down. That's shown in DXO's own numbers. There's a good thread about it, but the S9+ is absolutely not the best camera on a smartphone - it merely has the highest combined score so far, based on the new criteria which heavily favors having multiple cameras as opposed to a single lens. So there is now less emphasis on image quality and more emphasis on the more sensational and also more trivial aspects of photography that are enhanced by having a second lens.
Everyone said DXO was full of it when they scored the P2XL above everything else... either they were or they weren't. If they were, then they're just as full of it now. The fact is, as was realized then, is that the combined score is meaningless. It's the individual scores that actually give us good information and if you look at those scores, the P2XL trounces the S9+.