I've been doing more testing on this.

Definitely, the stereo image of phaser and flanger is not working
right. I was expecting 90º phase difference between the left and right
channels. Moreover, something similar can be achieved with the
ModFilter and the Xnob all the way up.

I can't understand why this was not implemented in these effects. Can
anybody explain why? Am I doing something really wrong? Can this be
fixed in a firmware release?