Agreed, but it seems to have something else going on in there too. Any idea?
Yo dude! It might sound like a flanger, but it isn´t.
It sounds like an automated Filter.
Not a flanger, more phasing if anything. You could try first filtering a track down to phone-like, leave that same track's end part un-effected (on the clip there there's some filtering on this part as well) and then cross-fade between these two. Play around with maybe nudging one of the regions/clips very slightly and see if that would work. Otherwise, some automated phaser and filtering would also prob work