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: 
Salam. Yeah it is a good question. Since you have asked it, I am pondering and searching about its answer. I could not get much references from Quran and Hadith but there is one Hadith in Sahih Bukhari as:

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> Bukhari :: Book 9 :: Volume 93 :: Hadith 597
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> Narrated Abu Huraira:
>  Allah's Apostle said, "A man who never did any good deed, said that if he died, his family should burn him and throw half the ashes of his burnt body in the earth and the other half in the sea, for by Allah, if Allah should get hold of him, He would inflict such punishment on him as He would not inflict on anybody among the people. But Allah ordered the sea to collect what was in it (of his ashes) and similarly ordered the earth to collect what was in it (of his ashes). Then Allah said (to the recreated man ), 'Why did you do so?' The man replied, 'For being afraid of You, and You know it (very well).' So Allah forgave him."
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Here the situation is a bit same but it would not happen for all humans the same. In that situation, the islamic scholars have agreed that if a person dies and is not engraved, His spirit or rooh will be tortured if he were a bad man and will be furnished with joy if he were a good man. Along his spirit his body will also be treated accordingly where ever it is.

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> The dead are to be questioned whether they are in their graves, or in any place; in the desert, the sea, or in the belly of a beast of prey. In all cases they will be questioned; their spirits will be questioned. They will be questioned and tortured if they are evildoers, and they will live in comfort and ease if they are pious. Their spirits will enjoy Paradise or suffer Hell. The remaining part of their body will go either to Paradise or to Hell in the way that Allah (Glorified and Exalted be He) Alone wills, but the spirit will suffer largely the torments in Barzakh (period between death and the Resurrection) whereas both the body and the spirit will suffer torment and pain or will feel happy and enjoy Paradise on the Day of Judgment.
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More over, Allah knows the best as He is going to give comfort or punishment to the dead. Could I help you or do you have some more to ask?
Qabar is name where body parts are found. It does not only mean a dig. So immidiately same procedure is applied.