How risky from a security standpoint is it to continue to use an iPhone 6? Will Apple continue to release security patches if exploits are found or do I need to shell out for a new phone to remain secure?
Basically apple does not release security updates after a major version unless it's a really extreme case.
I was in the same position and need to support several iOS apps and upgrade them to iOS13. I don't like buying new technology so I purchased a refurbished iPhone 8 with a new battery and screen.