My iPhone is saying iOS up to date and its iOS version is out of dat

Your phone is up to date. It can not run anything later than 12.5.6.

You need a new phone if you need a newer version of iOS.

Your iPhone 6 is up to date, iOS 12.5.6 is the latest iOS security update for iPhone 6.

iPhone 6 is an outdated iPhone it can’t be update to a higher iOS (13 and later).

The iPhone 8 Plus is discontinued. Apple no longer sells it.

The lowest price iphone currently sold is the iPhone SE, starting at US$429.