I strongly agree with your sentiment. As a Surface Book and Lumia 950 user, I have watched the Surface product line receive good attention and necessary quality improvements. Meanwhile, the phone space is all but ignored, with a curious caveat: for whatever reason, Windows 10 Mobile continues to see gradual updates and improvements. The core applications (email, music player, browser, calendar) continue to improve. So I remain a Lumia 950 user because, frankly, it does everything I need a mobile device to do.
But I am an edge case and broadly speaking, people want much more glamour from their mobile phones. At some point a few years ago, I think Windows Phone was up to about 5% share but it seemed Microsoft's work on mobile was put into slow motion. It's no wonder share has decreased since.
Continuum is a very good idea, but the progress on making it solid, reliable, and high-performance is astonishingly slow. I don't know the technical realities of the Broxton cancellation, but that really put a big kink in the notion of a real, solid Continuum experience. For the time being, it seems Microsoft is just hoping that HP can explore Continuum innovation with devices like the Elite x3. Virtually no one has even heard of an Elite x3.
Windows phone fans have been absolutely clamoring for an ultra-high spec glamorous phone. I think this is an artifact of everyone knowing one of the key drivers of phone adoption: make devices that catch other peoples' eyes and force them to ask, "What is that?" Word of mouth is a key part of adoption. I know when I purchased one of the first Lumia 920s (you might remember them as the very colorful Windows Phones from a few years back), many people would ask me about it. The 920 was hardly a success compared to iOS and Android, but it was probably the most successful Windows 8 phone, and I think that's in large part to it being something that people noticed.
Evangelists of the Windows platform have been eagerly awaiting a Surface Phone because they know it would be such a device. It would be a conversation starter. And frankly, despite it being a hard hill to climb, Microsoft hasn't been trying on mobile for years. They're not even interested in starting the conversation.
And that's a bit boggling and frustrating. I know several people bored of iOS, uninspired by the iPhone 7, and similarly disenchanted with Android devices. These people aren't vocalizing the words as such, but they are open to something new. If by some magic you could drop a Surface Phone onto the market with a rock solid Continuum experience, and put serious marketing effort into it, I think you could earn back that 5% share, and then work to grow from there.