you can use this phy settings in your stm32f4xx_hal_conf.h (RMII Config Tested FIne)
/* ################## Ethernet peripheral configuration ##################### */
/* Section 1 : Ethernet peripheral configuration */
/* MAC ADDRESS: MAC_ADDR0:MAC_ADDR1:MAC_ADDR2:MAC_ADDR3:MAC_ADDR4:MAC_ADDR5 */
#define MAC_ADDR0 2U
#define MAC_ADDR1 0U
#define MAC_ADDR2 0U
#define MAC_ADDR3 0U
#define MAC_ADDR4 0U
#define MAC_ADDR5 0U
/* Definition of the Ethernet driver buffers size and count */
#define ETH_RX_BUF_SIZE ETH_MAX_PACKET_SIZE /* buffer size for receive */
#define ETH_TX_BUF_SIZE ETH_MAX_PACKET_SIZE /* buffer size for transmit */
#define ETH_RXBUFNB ((uint32_t)4U) /* 4 Rx buffers of size ETH_RX_BUF_SIZE */
#define ETH_TXBUFNB ((uint32_t)4U) /* 4 Tx buffers of size ETH_TX_BUF_SIZE */
/* Section 2: PHY configuration section */
/* LAN8742A_PHY_ADDRESS Address*/
#define LAN8742A_PHY_ADDRESS 0U
/* PHY Reset delay these values are based on a 1 ms Systick interrupt*/
#define PHY_RESET_DELAY ((uint32_t)0x000000FFU)
/* PHY Configuration delay */
#define PHY_CONFIG_DELAY ((uint32_t)0x00000FFFU)
#define PHY_READ_TO ((uint32_t)0x0000FFFFU)
#define PHY_WRITE_TO ((uint32_t)0x0000FFFFU)
/* Section 3: Common PHY Registers */
#define PHY_BCR ((uint16_t)0x00U) /*!< Transceiver Basic Control Register */
#define PHY_BSR ((uint16_t)0x01U) /*!< Transceiver Basic Status Register */
#define PHY_RESET ((uint16_t)0x8000U) /*!< PHY Reset */
#define PHY_LOOPBACK ((uint16_t)0x4000U) /*!< Select loop-back mode */
#define PHY_FULLDUPLEX_100M ((uint16_t)0x2100U) /*!< Set the full-duplex mode at 100 Mb/s */
#define PHY_HALFDUPLEX_100M ((uint16_t)0x2000U) /*!< Set the half-duplex mode at 100 Mb/s */
#define PHY_FULLDUPLEX_10M ((uint16_t)0x0100U) /*!< Set the full-duplex mode at 10 Mb/s */
#define PHY_HALFDUPLEX_10M ((uint16_t)0x0000U) /*!< Set the half-duplex mode at 10 Mb/s */
#define PHY_AUTONEGOTIATION ((uint16_t)0x1000U) /*!< Enable auto-negotiation function */
#define PHY_RESTART_AUTONEGOTIATION ((uint16_t)0x0200U) /*!< Restart auto-negotiation function */
#define PHY_POWERDOWN ((uint16_t)0x0800U) /*!< Select the power down mode */
#define PHY_ISOLATE ((uint16_t)0x0400U) /*!< Isolate PHY from MII */
#define PHY_AUTONEGO_COMPLETE ((uint16_t)0x0020U) /*!< Auto-Negotiation process completed */
#define PHY_LINKED_STATUS ((uint16_t)0x0004U) /*!< Valid link established */
#define PHY_JABBER_DETECTION ((uint16_t)0x0002U) /*!< Jabber condition detected */
/* Section 4: Extended PHY Registers */
#define PHY_SR ((uint16_t)0x10U) /*!< PHY status register Offset */
#define PHY_SPEED_STATUS ((uint16_t)0x0002U) /*!< PHY Speed mask */
#define PHY_DUPLEX_STATUS ((uint16_t)0x0004U) /*!< PHY Duplex mask */
#define PHY_ISFR ((uint16_t)0x000BU) /*!< PHY Interrupt Source Flag register Offset */
#define PHY_ISFR_INT4 ((uint16_t)0x000BU) /*!< PHY Link down inturrupt */
it's work fine for me
