The third phase of the MCU takes place between 2016 - 2019 and comprises ten movies in total. If you'd like to watch the movies in chronological 'in universe' order, please view this timeline. It also includes the shorts and the TV series.
Phase Three introduces a second round of avengers. As the team continues to multiply, the main plotline comes to the forefront in Avengers: Infinity War, where nearly every character introduced over the course of the 18 movies makes an appearance. Together, they join forces to stop Thanos.
"Political involvement in the Avengers' activities causes a rift between Captain America and Iron Man." (IMDb)
"While on a journey of physical and spiritual healing, a brilliant neurosurgeon is drawn into the world of the mystic arts." (IMDb)
"The Guardians must fight to keep their newfound family together as they unravel the mystery of Peter Quill's true parentage." (IMDb)
"Peter Parker balances his life as an ordinary high school student in Queens with his superhero alter-ego Spider-Man, and finds himself on the trail of a new menace prowling the skies of New York City." (IMDb)
"Thor is imprisoned on the planet Sakaar, and must race against time to return to Asgard and stop Ragnarök, the destruction of his world, at the hands of the powerful and ruthless villain Hela." (IMDb)
"T'Challa, heir to the hidden but advanced kingdom of Wakanda, must step forward to lead his people into a new future and must confront a challenger from his country's past." (IMDb)
"The Avengers and their allies must be willing to sacrifice all in an attempt to defeat the powerful Thanos before his blitz of devastation and ruin puts an end to the universe." (IMDb)
"As Scott Lang balances being both a Super Hero and a father, Hope van Dyne and Dr. Hank Pym present an urgent new mission that finds the Ant-Man fighting alongside The Wasp to uncover secrets from their past." (IMDb)
"Carol Danvers becomes one of the universe's most powerful heroes when Earth is caught in the middle of a galactic war between two alien races." (IMDb)
The follow-up to Avengers: Infinity War. The plot is yet to be revealed.