I feel like there's still room for two more Phase 3 films since Phase 3 is lacking release dates in Q4 2018 and 2019. I'm surprised that they're doing Q1 films. Since Q4 courts the Christmas and Thanksgiving markets, I don't feel like well get a Ghost Rider film since doing one right requires an R rating. If these films happen, I wouldn't be surprised if the late 2018 film is a Hulk film and the late 2019 slot is for Spider-Man. Again, assuming that they happen. The only reason why these dates are empty is since marvel won't be footing the bill to produce and it'll be the job of Universal and Sony, respectively.
The 2020 films are presumably Iron Man 4, Black Widow and something else. I'm not sure what though, probably Fantastic Four if Marvel can get the rights back, if they can't get the FF back, I'm hoping it's Eternals as that's the last big property not owned by Fox that can't be done on a TV budget (save Hawkeye, Elektra, Moon Knight, Blade, She-Hulk and Punisher's solo adventures for TV, please). IMO, they need to end Phase 3 with one last ride for Downey before he hangs up the armor. They owe him that much.