I don't think there are any concrete advantages in using an old phone. If your phone isn't getting security updates anymore, you could be vulnerable to both old and new exploits. This particular vulnerability can be patched, for instance.
It's not necessarily a kernel issue, as nothing is inherently wrong with them; it's an exploit. If you put things that way, PC isn't any more secure, with threats like malvertising requiring zero interaction from end users to infect. Knowing what to do and what not to do will protect you against most threats you're likely to face, regardless of the platform you're using.