I had once a "Woop Woop Pull Up!" as a ringtone....yeah I know...
It did not last long, as I could see the scenario in IMC: "Disregard mate, it's only my cell phone, keep going...."
Still I cannot imagine what is more important on short finals than focusing on handling the aircraft, mind you at 700 feet, even a fire bell would be disregarded (silenced first) and treated as a ground emergency, so why a cell phone buzz is such a priority?
I would call any sim instructor sending me text messages during a check ride a sadistic bastard. This kind of example has been described in instructor courses as the "smiling assassin" model, and surely brings a note of negative training.
As for texting while taxiing or any other phase for that matter, I fully agree it should not be tolerated, but what do you do when it's your flight examiner who is still reading messages while LINING UP on the runway? You know what, I said nothing, when I get my checkride signed, I'll run the ship with what I hope are better standards than him. He switched off the phone after line up. I think we would have had an argument if he hadn't. I am glad I did not have to find out.
Back to the topic, if there was any fatigue aspect, leading to lack of managing priorities, it would be interesting not just to look at the last rest period and declare someone fit, but also getting the broader image of a week or two of duty before the event. Some work patterns though legal can turn a fully functional pilot into a hovering zombie...