Remove the battery, which I assume you have done. Take the top shell off. Immerse with a tap water, backing soda solution, in a sink, with a stopper. Use an entire box, of baking soda. Opinion varies, but do this for an hour, moving the parts around.
Then, rinse thoroughly under tap water. Dry with paper towels until you see no standing water. It is best to remove the ESCs and other PC boards so you can dry the backside. Do this to the battery too.
Then, go get a LOT of rice. Get a large bag that can hold your open Phantom and all the rice. Tie the bag closed. The rice will expand as it absorbs water. Shake the bag so dry rice will replace the swollen rice.
Leave it in the rice for 48 hours. Remove and if you see swollen rice underneath anything, either get more rice or get the swollen rice out of the bag. Then repeat for 24 hours, this time.
When it appears dry, use the paper towels anyway, then reassemble your Phantom. Hopefully, everything will work. However, the longer that the saltwater remains in the Phantom, the worse the corrosion. If it has saltwater in it as you read this, leave it in the baking soda mix twice as long. The baking soda changes the ph and helps with corrosion.
If it still has saltwater, in it, when you read this, leave it in the baking soda solution for several hours. Use at least one full box of baking soda. Mtwo boxes is better. I like to use warm water, so the baking soda mixes well.
Finally, I wish you the best! Please let me know the outcome.
Edit: As a last step, a hair dryer won't hurt. Just don't over heat any components. Use a waving motion and that will keep the components safe.