[warble]

From the referenced study: "The measurements were conducted in a diffuse sound field at a reverberant noise chamber at the NIOSH acoustic testing laboratory. The diffuse sound field ensured that the location and size of the smartphones did not influence the results of the study. "

Having done sound testing extensively, you can be sure in an airplane positioning and sound source and sound type can drastically impact your measurements. Multiple reflections can re-enforce, or reduce the measured level. The type of sound measured is very important as well.

He's not measuring pink noise on the airplane, what the measured level of a particular sound is, needs to be normalized to really understand what effects it will have on you.

I'm sure in a good test setup the smartphone can get you pretty darned close. I'm more concerned with this guy's test setup than the equipment used.