Why did he defend Phoenix from the full penalty for the crime he framed him for? I assume he would have gone to prison and then Kris could have checked him of his to stalk list for a long time.

I imagine that he planned for Phoenix to go to jail originally and defending him would be a great way to get Phoenix a conviction. He couldn't be certain what Smith had told Phoenix, so it would have been risky to leave Phoenix loose.

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He also did it to gain Phoenix's trust.

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That would also explain why Kristoph was the "only dissenting opinion" on the bar association's motion to revoke Phoenix's license to practice law. Even then, he wanted Phoenix to believe he had nothing to do with any of it. He was trying to pull the wool over Phoenix's eyes with his stylish three-piece suit.

Kristoph even says something to the extent of "Even from the beginning, you always suspected me, didn't you? You never thought our friendship was geniune."

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Why'd he go out of his way to help out Apollo then?

He has to at least put on a show of trying to defend Phoenix or people (Phoenix included) would become suspicious. Phoenix is supposed to be his friend after all and he can't make it look like he's trying to get his client convicted if he ever wants another job again. It would be very easy to subtly guide Apollo in a way that would lead to a conviction. If you mean why does Kristoph try to pin it on Olga after she incriminates herself, consider how important Kristoph's reputation was to him. If he had to lose (or make Apollo lose) to deal with Phoenix then so be it, but I'm certain with what we know of his character, that he would have preferred to keep his reputation intact. He could deal with Phoenix at a later time particularly if he still had Phoenix's trust, which until Phoenix attacks him, he had every reason to believe he still had.

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