According to the ESP32 reference manual, section 4.10, Table 4-3, the following pins are relevant for Ethernet using the RMII interface:
| ESP32 pin | Function |
|---|---|
| GPIO25 | EMAC_RXD0 |
| GPIO26 | EMAC_RXD1 |
| GPIO27 | EMAC_RX_DV |
| GPIO19 | EMAC_TXD0 |
| GPIO22 | EMAC_TXD1 |
| GPIO21 | EMAC_TX_EN |
| GPIO16 | EMAC_CLK_OUT |
| GPIO17 | EMAC_CLK_180 |
Note that typically the EMAC_CLK_180 pin is used to let the ESP32 create a clock internally using its PLL and output it to the PHY.
For an example schematic using the ESP32 EMAC with RMII interface, see the Olimex ESP32-POE schematic or the ESP32 Ethernet Kit v1.2 schematic