this is false. There was one phone [1], there was also a ROM for TT3 [2]. I have held each in my hands. The second link contains photos I myself took, in the real world of a real device.
Was that one phone actually commercially released by anyone? It just says that the OEM was shopping it around, so presumably more of a prototype than a final product?
A few of them exist in the real world - they gave out a thousand or so at PalmOS DevCon. To me that sounds like it shipped, even if in small quantity. These were not hand-built 3d printed prototypes. These were real devices with real injection molded silver plastic cases, operational slider mechanisms, working cell modems, and all.
I think "shipped" usually implies that one could buy them in some sort of official way. So for example the original chromebook CR-48 wasn't really "shipped" in that sense since you only got them as a devkit in conferences and similar, but the Oculus DK-1 "shipped" since even though it was a devkit you could buy it from Oculus.
At least that is the way I've seen the term used when it comes to development hardware.
[1] https://www.palminfocenter.com/news/7874/palm-os-cobalt-phon...
[2]https://www.reddit.com/r/Palm/comments/cjx9d9/palmos_61_coba...