Before I get into the actual fix for the phone, rice fixes nothing. In fact, it often makes things worse because you think you fixed it when in reality basically did nothing and the damage to the board gets to the point it is beyond repair for many people, which usually means replacing the whole phone. This is a waste of time and is a myth that somehow hasn't died yet.
The main thing to do with water damaged phones is to unplug the battery and cut off power as soon as you can. The problem with this on the iPhone is late model 4's and newer use a P2 Pentalobe, which very few people have in their toolbox. Most electronics oriented driver kits include it now, but it's still not common.
The first thing you want to do is to remove the battery to preserve your chances of repairing your phone. You can refer to this guide to do it: How to Replace Your iPhone 6 Battery
Once you remove the battery, remove the mainboard from the phone. The link to do this can be found here: iPhone 6 Logic Board Replacement. Once the board is removed, follow this guide as a starting point to clean the board: Electronics Water Damage
If you have access to a ultrasonic cleaner and solution to clean the board, this is the route I recommend taking to clean it. While it isn't worth going out and buying one for a one time project, it may not a bad investment. Not only will this clean the board more thoroughly and get under the chips, but it will improve the odds the phone will work again and is unlikely to fail due to delayed corrosion. The main reason I am suggesting an ultrasonic cleaner is it is NOT possible to clean under the chips with alcohol and a toothbrush.
If you want a low cost one and have more then one use case other then cleaning your phone, Harbor Freight sells a small one for $78.
The next thing to do is to replace the battery - do not clean this or attempt to reuse it. In most cases with water damaged phones these are compromised in some way. The damage is usually limited to runtime (and it's so bad you're forced to replace it anyway), but if the runtime is fine and the BMS is damaged you're asking for trouble.
While the board is out this is also a good time to clean the connectors for things like the TouchID sensor and camera modules. Since you already have the phone taken apart, this is also the time to check for damaged components in other areas and replace them before reassembling the phone. It's likely your speaker and headphone jack will be damaged, so I'd recommend ordering replacements when you order the battery. If you don't need them you have extras in the future.