I am guessing the advert you are referring to is the "Get lost in great stories" one [1] run in Vue cinemas. Other UK cinemas (Picturehouse, Odeon) mention the "big screen experience" but I think the Vue one is the only one that singles out that watching on a phone / laptop / TV can lead to a negative experience.

It's certainly one of the longer "please switch off your phones" messages, at over two minutes in length.

I used to enjoy seeing the adverts and trailers before a film at the cinema, but that was when I rarely visited. Now that I'm going much more regularly (sometimes multiple times a week), the lack of variety is very obvious: when I am forced to sit through the exact same collection of four or five adverts / trailers multiple times, it gets a bit old.