Hello,
The mdio tool you are using now is not able to work for 10G PHY.
Please use this one instead so that it can support C45.
phytool read IFACE/ADDR/REG
phytool write IFACE/ADDR/REG <0-0xffff>
phytool print IFACE/ADDR[/REG]
for C45:
ADDR := PORT:DEV
PORT := <0-0x1f>
DEV := <0-0x1f>
REG := <0-0xffff>