In October 2014, Marvel held a special event to announce all the movies that would comprise Phase Three, i.e. everything coming out between 2016 and 2019. There have been changes to the Phase Three slate since then like the addition of Spider-Man: Homecoming and Ant-Man and the Wasp, but nothing post-Avengers 4 in May 2019 has been revealed yet. Many fans have been eagerly wondering what some of the movies comprising Phase Four will be, but Marvel is continuing to be tight-lipped on the subject mainly because they don't want to give away what's coming up near the end of Phase Three.
Marvel Studios president Kevin Fiege told the Toronto Sun that the company already has a good idea of what the first Phase Four movies will be, which are being released on May 1, July 10, and November 6, 2020. We'll have to wait a little longer to find out what they are. In his words:
Where we go after Avengers; what those 2020 films are, we're pretty sure what those are going to be... but if I tell you that, we're getting into spoilers.
This concern about being too spoiler-y obviously wasn't an issue when the Phase Three slate was announced, as Avengers: Age of Ultron and Ant-Man hadn't come out yet to conclude Phase Two. This time around, though, it's a bit different. The end of Phase Three will also wrap up a lot of loose ends from the previous 11 years. Essentially, Phase Four is being looked at as a new beginning for the MCU. It will be a way to hit that refresh button while still keeping continuity intact. While Avengers 4's plot hasn't been disclosed yet, Avengers: Infinity War will see the eponymous superhero team and other heroes from the MCU teaming up to battle Thanos. Surely some leftover threads from there will factor into the fourth Avengers flick and the Phase Three conclusion, right? Keep in mind that both those movies could also see major casualties, and Kevin Feige presumably doesn't want to spoil who will bite the dust.
Despite the lack of specific details about Phase Four, there are some hints about what may be on the way. Movies like Guardians of the Galaxy 3, Doctor Strange 2, a Black Widow solo movie and the long-awaited Inhumans have been suggested or looked at as possible contenders for the lineup. Kevin Feige also recently said that Phase Four may focus more on making "intimate" movies rather than providing audiences bigger spectacles. At the rate we're going, though, it may be a year or two until we actually learn about what's in store for Phase Four.