Get tag phase on FX9500 reader

Is it possible to get the phase of a tag with FX9500 reader?

I work with Zebra EMDK for java, and when I use TagData[].getPhase() method, the result is always "0".

Is "0" the equivalent of "null", and the phase reading isn't support by FX9500?

Or is it a configuration problem in my code?

Thanks in advance.

Best regards.