Hi,
It's best to try this out playing multiple notes after each other. So first select a poly play mode for the Keyboard.
In Mono KBD mode each note retrigger the phase for all playing notes.
In Legato KBD mode legato played notes does'nt retrigger the phase, but all playing notes still play in the same phase.
In Poly KBD mode all notes retrigger the phase - but for each note you play, so each playing note will follow it's own phase. The phase for the playing notes will be different unless you hit notes to be in the excact same phase as other played notes.
Perhaps it's best to have a low rate, when you try this out.
I also assume this will answer your question about the Keyboard playmode setting.
Try it with different Keyboard play mode settings.
Also try with long envelope release time.
And also try while playing multiple notes at the same time.
All this will give you a feeling about whats going on.