My phone date showing as 12 August 2563 BE?

Your calendar format is set to Buddhist.

Go to Settings -> General -> Language & Region and change Calendar to Gregorian.

Go to Settings > General > Date & Time. Turn off Set Automatically and change the date to your current time zone.

I just spent a good 1/2 hour resetting and rebooting my phone with Apple Support and they couldn't figure it out and they hadn't been getting any calls but obviously I am not the only one.

Did yours happen when you updated to the new IOS ? I was able to see that 2563 BE is Buddhist time.

BUT! After speaking to Apple and having them inside my phone coupled with the fact that they aren't receiving a ton of calls, I tried my Carrier Sprint/T-Mobile and they were really helpful and agree with me that it's something to do with Google not playing well in the sandbox with Apple.

It doesn't surprise me at all that the latest IOS update had a component that made it more difficult to run both on an iPhone. So he suggested that I unsync my Google Gmail calendar from Apple. He said that i could still keep it synced on a laptop but not the phone.

So i'm going to try that and I'll tell you how it went