Had audio and video both on.

Phone Interview 1

Question 1
Given a tree, find level with maximum number of nodes.
Answer 1
Gave a BFS traversal solution, pretty easy to code. Interviewer asked about how will i test it, time complexity reason for choosing BFS.

Question 2
Given a sorted array find frequency of a given number.
Answer 2
I was confident on this, started with brute force then suggested binary search first and last occurance of the given element. While coding i got little confused with < and > logic, but after running an example completed the solution.

HR called and said in feedback that second question created some doubt in interviewers mind and suggested another phone interview, so i was given 5 days to prepare for another phone interview. Would like to point out facebook is not flexible in giving more preparation days. Although it should not matter as you should be ready but still HR strongly suggested not to take more than 7 days and gave me 5 days for both 1st and 2nd call.

Phone interview 2

Quesiton 1 : Find quotient and remainder for the given numerator and denominator without using /,%,*
Answer 1: I gave the simple solution using + and -
Interview asked to optimize I suggested using bit operation but could not present a clear approach
Question 2 : Interviewer allowed to use * to calculate quotient and remainder.
Answer 2: I struggled but stumbled upon binary search, wrote code interviewer was satisfied.

Got a reject call from HR after 5 days.
The reason I think was, I was not quick enough.
Binary search is something often overlooked. I would suggest to even practice questions that are heavily downvoted if they are tagged in some company you are appearing for.

Questions/ variations can easily be found on leetcode.
This community has helped me a lot, Hope this post helps.