Any time you believe your phone has water damage it is best to bring it in a shop for a cleaning asap. If the water sits it could potentially create rust and corrosion to your device very quickly or short circuit the device. Turn it off and keep it off till you can do that. As for cracked back glass. That will generally be mostly cosmetic damage unless the wireless charger is exposed(it has a copper color and is roughly in the center of the phone). Back glass replacements aren't necessary and is ultimately up to you.
Feel free to bring it in to the store for a free diagnostic. We can try our best to evaluate and quote you a price in store.
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