No are you because it was a direct hit its takes time for him to phase through something an Minato has proved that just as the Amaterasu was a direct hit he could not phase through a direct hit
You do know you're wrong right? Obito took direct hits when Konan mixed explosive tags with her paper when he tried to warp her (has to be solid to warp others) but he quickly switched to absorbing the blast which saved him and Konan from dying
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. Amaterasu has shown to burn things rather slowly and some avoided death as shown with Tobi, A, Trees Itachi hit, Karin, Bee, Edo Nagato, Juubi, Juubito. The moment Amaterasu hit him he could absorb it since it's like a vortex as shown here
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.Also if you're talking about Juubito being hit by Amaterasu, Juubito can't use Kamui cause he was the Juubi's jinchuuriki, Obtio said this when Naruto hit him with SM Rasengan
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Obito can't kamui something on his back. He was forced to used izanagi...As said by konan to kamui anything he has to become solid. then would be burnt from the flames...Later whenn obito came out he had no burn marks what so ever
Actually he can, when he warps it like a vortex as shown in Konan verse Obito, he went from intangible to solid to warp Konan which took on a vortex form
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. Obito was able to absorb the explosive tags blast fast which does damage faster than Amaterasu which has shown to burn things slower than the few small things it shown to burn a bit faster.Danzo had to use hand signs each time he used Izanagi and it didn't chance his clothes from before using it to after
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. So even if he used Izanagi after Amaterasu then his shirt would still be burnt since it wouldn't have taken affect until Obito active the jutsu but he could have started to warp the flames as he fell in the darkness.