I, personally, think that you all are underestimating the circumstances under which Obito had to phase "his whole body" like,
Example One:
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As you can see, Obito's full body does seem to phase but there are other factors to take into rather than the fact his entire body is "ethereal". Such as the situation this happened under, Gai threw a kick, one that would have been problematic if Obito would have let it hit. Meanwhile, Kakashi is trying to get Naruto out of Obito's clutches, this is all happening very fast by the way. Now think, Obito had the intentions of warping Naruto instead of using the Human Path to kill him, as he's stated multiple times in the fight."You two have something that belongs me." The Tailed Beast. He preferred for the Ten Tails to be fully revived, if possible. Not to mention, Obito is a sensory shinobi, so he probably sensed the two senseis, no matter how fast they were. So he probably was prepared, and expected this. He had no way of warping Naruto, therefore winning with "one touch", His warping was not fast enough to warp Naruto before Gai and Kakashi could intervene, plus, even if Obito did attempt to warp, Kakashi and Gai could have easily attacked, stopping him. Due to the fact that Obito is confirmed to be solid when warping either himself or others. Obito was not foolish enough to do such actions.
Example Two:
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Again, this is an example involving the very same opponents in the previous example, so, the same logic could be applied. He was likely wanting to warp Naruto for the same reasons stated above, in short to make the Eye of the Moon plan go smoother. He needed Naruto alive for the Tailed Beast to be extracted. Now, again, Obito was a sensory shinobi, meaning he most likely sensed Gai and expected this, to a degree, but you have to look at the circumstances for Obito, Gai was close by planning on interfering and him grabbing a Naruto and warping him without such restraints unlike last time would have been even more difficult. So, instead of attempting to warp Naruto and getting stopped by either one, due to his warping speed likely not fast enough to avoid failure, he decided to simply phase past Naruto and continue on with the battle. He knew he likely had more chances to get Naruto or Killer Bee, so he phased in both examples just because he knew it wasn't the end.
Now, thanks to others in the thread, you all are aware that Obito "broke the rules" due to images proving this, but this may be something Obito is truly capable of, not some mistake by Kishimoto, so next time you see Obito and think he's going full body "ethereal". Remember the circumstances Obito was under, would it have really been profitable to continue in an attack likely to backfire? Obito was bound to see that these situations would have proved fruitless, so he decided to phase through it all and hope for the best.