DP83869HM: Is RX_CLK sychronized to the transmit clock of the partner in RGMII to 1000Base-X mode ?

Hi,  In my application I need local reference clock to be phase-locked to the partner, which is a 1000Base-X transmitter. So DP83869 is in RGMII to 1000Base-X mode.

Sometimes I found that local reference is out of lock with the partner now. Maybe it's the issue of PLL circuits. But firstly I need to confirm the source of RX_CLK. So, I need to make clear the following questions:

(1) Is RX_CLK recovered from the receiving stream and locked to the peer's transmitting clock instead of being synchronized local reference?

(2) What is the difference between RGMII-to-1000Base-X and RGMII-to-SGMII when connecting to an SFP module? I found that link can both be up normally and throughput is good when DP83869 is configured as any one mode of these two.  

Thanks.