If Kat is the next target in the tribe I think it's simply because she's in a minority and isn't so good at challenges. The 'flipper' storyline we heard in the episode didn't convince me. You're only really a flipper in Survivor if you change alliance a few times, and she was never part of the main alliance in her original tribe anyway. And she gave them useful information on the immunity idol.
Rohan giving it to Phoebe to play was actually a great move, I wonder if he had an idea that it was her and not him that was the main target. His edit though was very much the horrid person who wouldn't give his idol to Phoebe lol.