Greedy Algorithms

Reading Material

Chapter 6 of Antti Laaksonen's Competitive Programmer's Handbook (available online for free here)
Chapter 3.4 of Steven and Felix Halim's Competitive Programming 2 (available online for free here)
Some editorials of your choice from GeeksForGeeks to get used to the greedy approach and how to apply it in different problems.
If you have time, Jeffe's Greedy Algorithms to get used to the mathematical proof of greedy algorithms, which is a very important skill to have.
Advanced but more Math-oriented, Olympiad Combinatorics - Pranav A. Sriram

For those who follow the roadmap, come back to the last book in the midde of phase 4 or later.

Side-note : reading some editorials will help you grasp the concepts, but solving problems is the key to mastering greedy algorithms.