As Martin implies, I’m not sure that the airlines are that bothered.
On Emirates as well as BA LCY you can also use your phone in flight, so presumably they aren’t that fussed (safety wise or socially) that people are using them.
I doubt they would install jammers as the people most likely to be using them are those in premium cabins who apparently keep the airlines going these days…..
On Canucklad’s point, if you are sitting towards the back of a 777 you have plenty of time between leaving the active runway and exiting the plane – usually at least 15 mins. Certainly enough time to check texts, emails etc. Of course this can all be done with the phone switched to silent.