It's only the last few years that the festival have started calling it the Legend Slot. For most of its existence it's been the Teatime Slot, with the idea it was the sort of music that Jean Eavis liked to listen to whilst having tea on a Sunday afternoon i.e. MOR, Radio 2, borderline easy listening sort of music. Hence bookings like Shirley Bassey, Neil Diamond, Tom Jones, etc. There's mibbe some overlap there with classic radio rock and of course the boundaries are all pretty fuzzy now, but it's generally not a rock slot.
I've never had any issues. Remember watching some Tour De France stages on phones in the past. Maybe at the festival sight it could be a problem, but I think people are spread out enough on camping.
Maybe it will be different this year with only teenage girls coming to see The Cure, David Byrne and Napalm Death 😅