I'm having a similar issue to that raised on the DP83640 but with the DP83630 namely "an invalid checksum generated with SYNC_1STEP". On the PTP_TXCFG0 register I have the following bits on

SYNC_1STEP | CRC_1STEP | CHK_1STEP | TX_IPV4_EN | TX_PTP_VER | TX_TS_EN = 0x8625

I've just added the CRC_1STEP bit in line with the DP83640 question. What are the 2 bytes that should be zero? 

I was expecting that if I output the UDP checksum as zero then the PHY would update the checksum with the correct values. If I force the checksum to be zero and override our network stack which is trying to replace a UDP checksum of 0x0000 with 0xFFFF I no longer see an error but Checksum is declared as uncalculated on PTP Track Hound - PTP slaves now sync, but I'm not happy that this is the correct solution.