Anyway. grepping for tthat property in the OpenWrt source shows that it is used by the driver for that rtl8367b device. It's loaded by this function with "name" = " realtek,extif0":
So the short version is that this is an obscure and proprietary way to set these 9 phy properties. The names in that function should be pretty self-explaining? Each of these should have had a designated self-explaining property in the DTS too. In fact, I believe there are standard properties that could be used.
But this is probably a driver originating from som vendor source, with the strange quirks that follows