Sorry, but it's all bollocks!
If there was any real risk, at all, to safe flight do you really think they'd rely on the SLF to 'please turn off your phones'??!!
No, if it was a serious issue the phones would be removed at security and placed in a lead-lined box (or whatever) for the duration of the flight.
So, my simple deduction - it does not have, and never has had, any safety issues whatsoever.
I'll duck behind the parapet now!
Fly safe, phone on or off, Sam.