Google has been very quiet about what SEOs have been calling the "Phantom update." The Phantom update has been floating around for the past couple years now, and we've covered it multiple times here. In fact, Glenn Gabe has likely done the most analysis of these so called phantom updates.
In any event, Google's Gary Illyes kind of said on Twitter that these Phantom updates are the same as Google core updates. Meaning, these are basic quality updates to the search algorithm that Google will not confirm.
Roger Montti asked him about it on Twitter and he responded:
@martinibuster very. core update == phantom ¯\_(ツ)_/¯— Gary Illyes ᕕ( ᐛ )ᕗ (@methode) March 21, 2017
Interesting admission? Of course, we can't know for sure if ALL the reported Phantom updates were "core" Google algorithm updates or just some.
Glenn Gabe I believe did name it and he confirmed it:
But yea, we can just speculate what these updates were if Google won't comment on them. Can you blame us?
No, I don't think the Fred update is a Phantom update.
Forum discussion at Twitter.