Using a cell phone during davening or when a Rav is giving a shiur (whether answering it or texting or looking at the text) is worse than those kids who text on Shabbos.
They’re both bad; why do you think this is worse?
The exception of course is Pikuach Nefesh.
Then during davening or a shiur is better than on Shabbos? (I’m not sure I got your last point.)