This is a troublesome step, since the LCD connector is particularly difficult to reconnect, and know that you've gotten it on. And thanks to the note claiming that if it's disconnected, if you might just get a black screen, you're left with having to disassemble the entire unit again, without knowing if it's powered off (since you presumably tried to power on). That's also nerve-wracking. I had this problem and disassembled and reassembled the entire phone, only to have the problem again. On the second try, I plugged the phone into power, and after a little bit, got the dead battery screen showing. So the problem was that the battery was discharged, not that I'd biffed the LCD connector.
I had trouble with this step too, since I had to apply quite a lot of force on the suction cup when pulling up on the screen while holding down on the frame with my fingernails. Eventually it popped free, but came almost to 90 degrees before I was able to stop it. No damage, but nerve-wracking, and if there was a better technique, it would be good to figure it out and share the information here.
Just a quick note that if you're doing this teardown because your iPhone 5 isn't charging unless you apply some force to the Lightning cable, the problem may simply be some lint or other crud in the Lightning port. Blow some compressed air in there before you disassemble your iPhone and see if it solves the problem - it did for me.