I went through two phone interviews. Amazon focuses highly on data structure related questions - linked-list, tree, BST, hash table etc. Among the 2 phone interviews, the 1st one was pretty easy - basic algorithm questions, concepts like your understanding of time complexity - simple problem to solve. I think they just test if you have basic knowledge of computer algorithms and you can write code. The second phone interview was a bit more advanced. It was on data structure and object oriented programming concepts - problems on data structure, OOP concepts. The phone interviews were 45 min long and asked to solve 2/3 problems.

One online assessment and one virtual interview included a coding round and leadership principle questions; overall, the process was fairly straightforward and not overly challenging for me throughout the experience.