ST supports several Ethernet PHYs. For others, you need to make the code changes yourself. For most MCUs, LAN8742 with RMI support is the most likely option.
Since you have to deal with all software processes for alternative Ethernet PHYs, you can choose the PHY you want.
You will need to detect the differences between the PHY you have chosen and LAN8742 or DP83848 and edit these differences in ethernetif.c/h files.
Once upon a time, CUBEMX allowed you to enter address definitions for the PHY you wanted.
