Fiddler and Les Mis both have a general rush, i.e. anyone can get those tickets, not just students.
I'd say both should be fairly easy by now, but that's just my gut feeling and the fact that it's summer and a lot of tourist are in town might make it harder. You could search this board for topics specially about rush reports on those shows and see what people have been saying.
Phantom only has an online lottery. That means you enter until a certain time (usually around 3pm for an 8pm show), then they'll draw winners and notify them within 5min-1h . I haven't done the Phantom lottery so I don't know how this one specifically works.