I hear this announcement on trains (which I ride a lot of) all the time and it always stands out to me, especially since I can't ever (consciously?) remember encountering outside of this specific use case. From my understanding, and searching online and reading stuff like this webpage, 上 in this context is used to mean "after", e.g. literally "after setting [your phone] to silent mode…" But what's the difference between this and から, or 後に, or other alternatives? Is it only used in high-formality situations? How about occurrences in speaking vs. writing? What other instances have you seen/heard this used?
Finally, back to my specific example of「車内ではマナーモードに設定の上、通話はご遠慮ください」, why wouldn't they simply tell people to set their phones to silent and refrain from talking? Why 'after', i.e. why use 上 at all? The sentence's meaning (and pragmatic goal) doesn't seem to change too much without it. Is it a specific expression/set phrase, but just an arbitrary choice out of other equally-natural-sounding possibilities that could have been used for this type of announcement… or is this really, definitely the most felicitous/natural phrasing choice for native speakers when expressing this message to customers, in this context?
Thanks!
by frozenpandaman