Does latest ios version gets updated on all the iphones
iOS 11–12 are supported on all iPhones since iPhone 5s (2013)
iOS 13 is supported on all iPhones since iPhone 6s (2015)


Generally support is for n-1 from the latest major release of iOS. If you support iOS 12, you'll include every device since iPhone 5s. It's assumed people will be running the latest or n-1 version of iOS on their device.