A few decades in the industry, repairing a lot of phones that were dropped into a lot worse than ocean water, taught me a few things.
Alcohol is not only anhydrous if it's 99% (has almost no water [open the container of 100% alcohol and, unless the humidity is 0%, it's no longer 100%), it's hygroscopic - it absorbs any water it comes in contact with.
Being liquid, it can dilute and wwash out impurities - such as the salts in sea water or whatever gets into the phone when it's dropped into a toilet.
It's not the water that causes the damage, it's the impurities. Pure water (water made by combining hydrogen and oxygen and kept in a pure state) is non-conductive and non-corrosive. It wouldn't have much effect on a cellphone, as Aglet's experience bears out. But we seldom drop our phones into pure water, so the important thing is to immediately (before doing anything else, unless it's saving your life) stop the flow of electricity (which, flowing through those impurities, causes the damage), then wash the insides of the phone out with a few changes of alcohol - 70% isopropyl that you get from the store is hygroscopic enough. (If the phone doesn't have a replaceable battery, which is cheaper - having the cut-out battery resoldered and putting a new case on the phone, or replacing a non-working phone? Break the back enough to be able to cut one of the battery wires.)
Putting a wet phone in dry rice (silicon gel is better, if you have enough - so is a hearing aid dryer) just delays the inevitable. The impurities have hours to etch the copper on the motherboard (and any other boards) and every time the humidity goes up they get wet enough to get another shot at it. Current flowing through a salt trail between conductors forms a carbon trace that forms a short. Eventually, even though the phone's been working for weeks, or even months, it suddenly stops - and you have a phone that no reputable shop will even attempt to repair. To save $5 on a few bottles of alcohol? (Or even $100 to replace the broken back on a $700 phone?)
I don't know who came up with the dry rice bit (I heard it more than 10 years ago, at least), but it wasn't someone who repaired phones for a living. (Maybe it was someone who sold them.)