Taken from the r/MobileRepair subreddit’s Rice Bot: “Somebody said "Rice". If you're talking about a water damaged device, I hope you know putting it in rice is just a myth. Rice is unable to pull moisture from inside your device. While waiting for the rice to do it's magic trick you're letting that moisture form corrosion. This corrosion can and will cause short circuits. If you truely would like to save your device please take it to a reputable repair shop immediately and do not try to charge or power your device on. Applying power will cause the corrosion to happen quicker by elecrolysis. If you have a removable battery please take it out. Rice is the homeopathy of mobile repair or as /r/MobileRepair calls it Holistic Phone Repair.” You need to get the phone to a shop ASAP so they can clean the corrosion and identify and other issues that it could have caused.
It is a known issue with the Baseband IC on the logic board, this is not a DIY repair. There are professionals that do this kind of work but it will likely cost about as much as buying another iPhone 6.