I was recently on an airplane when the flight crew seemed quite upset. They even threatened to return to the gate if passengers did not place their phones in airplane mode.
I took a private plane once and when I asked the pilot about switching off the phone, he said it did not matter to him because it had no effect and told me that if the phone signal could connect with a tower, then it was ok to make calls. He said the rule was for commercial airlines only because due to the high number of cell phones on a commercial jet, the volume of signals being transmitted at one time could affect instruments.
I’ve sat next to pilots in coach and I’ve seen them use their phones (not to make calls) but do not know if they are on airplane mode. I tend to use my phone and switch it to airplane mode as the jet is speeding up the runway and have never been questioned. If you think about it, there are millions upon millions of passengers worldwide on thousands and thousands of flights and not a single plane as far as we know, has suffered an issue.