Alcohol is fine.
Well...that actually depends on which form of alcohol you are talking. 99% IPA? Absolutely fine. 70% rubbing alcohol from the drug store? Should be OK but it will probably leave streaks from the high water content.
Most of the people who say not to use alcohol have no idea what they are talking about and are just repeating what they think they have heard. You have to remember than an iPhone screen isn't an LCD on the outside. Its either Gorilla Glass or a knock off. Alcohol will evaporate way before it has a chance to chemically react with the glass. But even on a naked LCD without any glass, OCA or polarizer, 99% IPA is what I used to clean them with.
With all that being said, I use Zeiss lens cleaner on the phones that I work on. Mostly because I don't want my customers opening up their new phone and being hit with a blast of alcohol. Instead it just smells clean.
To sum it all up: use whatever you want. I've tried damaging screens with random chemicals because...well...I have issues. The worst reaction I got was from leaving 99.9% acetone on a screen overnight and all that did was make a white mark.