default or selected kernelversion does not have config value CONFIG_MTK_NET_PHYLIB.
Result is shown for kernelversion 6.6.75

CONFIG_MTK_NET_PHYLIB (not configurable)

modulename: mtk-phy-lib.ko

configname: CONFIG_MTK_NET_PHYLIB

Linux Kernel Configuration
└─>Device Drivers
└─>Network device support
└─>PHY Device support and infrastructure
└─>MTK_NET_PHYLIB
In linux kernel since version 6.13 (release Date: 2025-01-19)  
source code:
drivers/net/phy/mediatek/mtk-phy-lib.c