The major difference between Phase Three and Phase Four: Unless Black Panther: Wakanda Forever is very different than we expect, there won’t be a huge storyline-ending capper to the phase.
In comparison, Phase One lasted six movies, Phase Two lasted six movies, and Phase Three lasted 11 movies.
That’s the word out of Comic-Con, where Marvel’s Kevin Feige announced to the crowd that the last movie in this latest era of the MCU is Black Panther: Wakanda Forever.
Phase Four of the Marvel Cinematic Universe is over.