Marcin,
Unfortunately, we do not have a reference design that uses the LAN8720.
Looking through your connection proposal, you will need to make a few minor adjustments. If you look in the LAN8720 datasheet (http://ww1.microchip.com/downloads/en/devicedoc/00002165b.pdf), there are two connection schemes listed. Figure 3.7 shows the connections when using an external 50MHz clock source. In this case, nINT/REFCLKO is an interrupt and should go to a GPIO pin on the OSD335x device. Additionally, you need to be careful in layout to make sure that the clock is balanced between the PHY and the OSD335x. Figure 3.8 shows the connections when using a 25MHz crystal. In this case, nINT/REFCLKO is used as a reference clock that should be sent to the OSD335x.
Figure 3.8 is what is shown in the first picture you attached from the reference design. If you would like to use the 50 MHz oscillator, then you will need to remove R11 in your diagram and connect the nINT/REFCLKO to a different GPIO pin that you will specify as the Ethernet interrupt in your device tree. Alternatively, you can change the 50MHz oscillator to a 25MHz crystal and use the connections from the reference design.
Regardless, you will need to add the appropriate pull up resistors (i.e. the 10K resistors in the reference design picture) in order to set all the strap pins. Additionally, you will need to add the 1.5k pull up resistor the the MDIO connection per the Ethernet specification. Also, it is a good idea to add the 33Ohm termination resistors to help with signal integrity on the interface.
Please let us know if you have any additional questions on this.
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