R' Eliezer Melamed, in Peninei Halacha, Shabbat 23:4, sounds similar to your citation from the Shemiras Shabbos Kehilchasa:
Included in this category of muktzeh are: musical instruments, smartphones, radios, tape recorders, expensive or fragile music players, cameras, and mixers. These may not be used even for a permissible purpose, for example, as a paperweight. Similarly, one may not wrap himself in an expensive piece of fabric that has been set aside for sewing. In contrast, a valuable or fragile item that is frequently used on Shabbat, such as a gold watch, eyeglasses, or a magnifying glass for reading, is not muktzeh.
Interestingly, the web version of the original Hebrew of this paragraph opens with a shorter list of devices: "musical instruments, handheld computers, cameras, and mixers."
בכלל מוקצה מחמת 'חסרון כיס': כלי נגינה, מחשב כף יד, מצלמה ומיקסר.
It is notable for the purpose of this question that R' Melamed is a rabbinic authority who is reputed to be particularly in tune with contemporary realities and issues. Indeed, the English website for his Peninei Halacha series ascribes to it "an emphasis on relevant issues which have arisen in the modern era."