It is common to find microcontrollers with an integrated 10/100 Ethernet MAC and PHY. Some microcontrollers, such as the Texas Instruments TM4C129x series, offer both an integrated PHY and RGMII interface for external PHYs, shown in the figures below:
(c.f. this datasheet (PDF))
The external PHY would then be something like a Micrel KSZ9021RL (PDF) or Realtek RTL8201. The internal PHY would just be connected to magnetics and a jack.
What benefits are there to using an external PHY over an internal one if both are available? It seems like using the internal PHY saves on BOM and significantly on PCB routing.