This isn't a Qatar Airways only problem, sadly. It happens on all airlines all the time. I think a lot of crew have got fed up of telling pax to stay seated or keep their phones off, so have given up doing so. It makes it difficult or those who do tell the pax because it makes them [the crew] look bad. Passengers need to realise that when they're on a [airline] aircraft, they have to abide by [airline]'s rules, without question.