That's good advice (they can see your cell phone from different angles). I had a friend let me in on this at the beginning of my play, and I thought he was nuts. Since then I have the screen "brightness" turned way down (thanks for the help on that kids...), and only get it out if there is a wall I can turn my back to and hold it at 90 degrees to the floor. Otherwise, keep your notes in your head and record it in the bathroom. Here is what I keep:

Each shoe: Dealer and pit name, including physical description, cut depth, speed of dealing, number of hands at different counts (approx), wonged in/out, number of players at the table, starting and ending $, bet spred used, any information about the dealer/pit that could come in handy another time (family info, past job, hobbies, etc.), also any "opportunities".
Each visit: record all of the above in proprietary software, along with grouping "sessions" (group shoes), record all expenses including mileage, food, hotel, tips, etc.

Come tax time it should help, and also helps in developing what dealers/pits/casinos to travel to on what shift and what day.