I've been looking at ways to teach students on this issue. Here's some stuff.
1) Experiments that illustrate the ineffectiveness of multi-tasking. For example, time yourself writing the word MULTITASKING, and then number the letters. So your final product would look something like:
M U L T I T A S K I N G
1 2 3 4 5 6 7 8 9 10 11 12
Record your time. Now Round 2. This time rather than writing the word and then numbering, alternate between letter and number. M, then 1, U, then 2, L, then 3, and so on. Spoiler alert: it takes significantly longer the second time. You might find there is a loss in the quality of the written product the second time, too. We did this with students but had them write something a bit longer so it would really illustrate the point. Now imagine you're working on a hard math project but you're switching back and forth between that and a text conversation. What are you costing yourself? How are you limiting yourself?
There are probably other fun challenges to do with students that would bring this point home even more. The reason multi-tasking doesn't work is because our brains don't think in serial fashion like a computer. Our working memory is more like a slate or a whiteboard that gets partially wiped clean every time we switch contexts.
2) Take an inventory of your screen time. There are apps that give you really good visual data on how many times you check your phone, how much time you spend, broken down by task or by app you are using. I am trying QualityTime for Android right now. Moment Screen Time Tracker is a popular one for Apple devices. Here's a fun little Buzzfeed video about this. It would be great to get students to try this and take an honest look at their phone use and see if it aligns with their priorities and their passions.
3) I mentioned the Pomodoro Technique in another thread. The idea is you work in short, uninterupted bursts, and then take short breaks. For many students it would be a great success if we could teach them to be able to disconnect for up to 20 minutes in order to allow themselves a chance to experience uninterrupted, deep conversation, deep reading, etc.