Most USB controllers have the physical layer signalling part
(commonly called a PHY) built in. However, dual-role devices
(a.k.a. USB on-the-go) which support being USB master or slave
with the same connector often use an external PHY.

The drivers in this submenu add support for such PHY devices.
They are not needed for standard master-only (or the vast
majority of slave-only) USB interfaces.

If you're not sure if this applies to you, it probably doesn't;
say N here.

source code:

drivers/usb/phy/phy.c