UPDATE: Kevin Feige confirms Marvel's full Phase 4 runs only two years
It seems Marvel Studios sneakily announced the Marvel Cinematic Universe Phase 5 slate at San Diego Comic-Con 2019. Several years ago, Marvel Studios president Kevin Feige held an event, separate from Comic-Con, at Disney's El Capitan theater in Los Angeles, where he announced the entire MCU Phase 3 slate, beginning with Captain America: Civil War and concluding with Avengers: Infinity War - Part II (later renamed Avengers: Endgame). Of course, things changed along the way, and Phase 3 ended with Spider-Man: Far From Home.
But due to spoilers and wanting to conclude the Infinity Saga on the right note, Marvel Studios refrained from revealing their MCU Phase 4 slate until after Spider-Man: Far From Home was already in theaters, and the best place to do that was obviously San Diego Comic-Con. During their Hall H panel, Marvel unveiled their entire Phase 4 lineup, starting with the Black Widow movie in May 2020 and apparently wrapping up with Thor: Love and Thunder in November 2021.
Even though Marvel only announced release dates and time frames for two years, they actually confirmed 10 projects in total, which is technically one more than they had on their original Phase 3 slate but one less than what they ended up with (thanks to Ant-Man and Spider-Man). Considering that Marvel referred to this list of movies as Phase 4, explicitly named them Phase 4 on their calendar, and has roughly the same number of projects coming out, it stands to reason that everything else they mentioned is coming in Phase 5.
Remember, the Disney+ Marvel shows are being made by Marvel Studios, not Marvel Television. These series will directly tie into the movies - the upcoming WandaVision series leads straight into Doctor Strange in the Multiverse of Madness, which hits theaters in the same season - so they are expressly considered part of Marvel's Phase 4 slate. Taking that into account, that means Black Panther 2, Captain Marvel 2, Guardians of the Galaxy Vol. 3, Fantastic Four, X-Men, and Blade are all part of the MCU's Phase 5 schedule.
But that must not be the entire slate, seeing as there will most likely be additional Disney+ TV shows parsed throughout. While it seems strange that Marvel would announce their Phase 5 movies along with Phase 4, it makes sense when looking at the release dates. They already have dates set through 2023, but with Disney's streaming service on the way, they can shorten the span of each phase while still delivering on the approximately the same number of projects.