Question: I want to ask that people who are not buried after death like if they died at sea or burnt but not buried, how they are answerable to munkar nakir and how they would go through their phases of grave?

Answer: 
Qabar is name where body parts are found. It does not only mean a dig. So immidiately same procedure is applied.
As far as punishment for soul those who body is burnt seems to have some validity but what about questioning in grave and all the fear that mullah puts in your heart about grave. that does not seem to apply to those whose body is never buried in grave.
Please only reply with sahi hadith with reference or from quran with reference do not just say what your little head think and understand