It says a lot about Marvel's achievements with the first 3 phases of its cinematc Universe that we all really want to know what Phase 4 will look like. I mean, we REALLY want to know. There is so much demand for an answer that Marvel head Kevin Feige keeps trying to address the swirling rumors by not revealing too much and, sometimes, just stating that there is no plan to unveil a new phase at all. Maybe there just isn't.
Phase 3 is supposed to end with an Avengers double-header "Infinity War," and its sequel "Infinity Gauntlet," post-that it will become a little clearer and we'll be able to decipher what's next for the Marvel Cinematic Universe.
Meanwhile Feige is hinting that there might just not be a fourth phase and that he will, most likely, let all the movies play out and decide the overlapping of characters as they go along. I do like that concept, instead of feeling forced just let it all play out and connect the dots, if they even need to be connected.
Here's what Feige had to say:
“I think people like to talk about our long term plans, which we certainly have. But very rarely do those long term plans dictate the specificity of any individual film. It’s usually the opposite. It’s focusing on a story, and focusing on the individual movie that we’re making to do what’s best. And then, if something changes that we weren’t quite expecting down the line because it was made for a better movie, then we deal with it down the line. I think that’s what happened in Phase One. We were telling those stories and having the crossover of Nick Fury talking about the Southwest Region, when the hammer fell…”
[Screenrant]
Right now a non-connected/overlapping "Phase 4" might look a little something like this:
"Guardians of the Galaxy Vol. 3"
"Black Widow"
"Doctor Strange 2"
"Nova"
"Spider-Man: Homecoming 2"
"Secret Avengers"
"Black Panther 2"
"She-Hulk"
"Captain Marvel 2"
"Fantastic Four"