It's a type of phase too, in the sense that he is someone Reina admires as a musician and she could be infatuted with him because she wants to be as good as him. Also the fact that she has no chance for him.
But Reina's reactions to Taki are different and more blatantly romantic than with Kumiko. This, plus he is a man, so it is viewed as more serious.
Yeah, you're right. Even though its an unrequited love from Reina and it would lead to nothing, its still treated like something more serious than just an extremely close friendship.
It really is a shame that this is going to end in heartbreak for all of the yuri fans. I wish KyoAni would just deviate from the source material and gave us the ending that makes the most sense in this series, which is ReinaxTaki, err, i mean ReinaxKumiko.