That is nice phaser effect that can run in stereo mode. The app is Audio Unit AUv3.
In stereo mode the signal is split and run through 2 phaser effects with different frequency settings but same rate, depth and feedback that are shifted in stereo space with the same rate(same as the phasers’)

The app is an Audio Unit Effect AUV3 and can be used inside GarageBand or other AU host apps as an effect plug-in. Stereo Phaser can also run as a stand alone app adding effect to the audio input so you can play your guitar, bass or synth directly through the app if you have the connector to do so.

Stereo Phaser controls:
- Rate - that is the phaser speed
- Depth - phaser depth
- Feedback - effect feedback
- Stereo - stereo spread