Hi, Derek,
I think all the Kinetis boards use the same PHY KSZ8081RNACA, we only have the driver based on KSZ8081RNACA. If you use LAN9354 as PHY, it is okay, but you have to write the driver yourself.
The LWIP ethernet stack uses clear layered software architecture, you only need rewrite the fsl_phy.c and fsl_phy.h.
Hope it can help you.
BR
XiangJun Rong