What do I do with this Oncidium?

[bo1075]

I just received this in spike Oncidium Sharry Baby 'Sweet Fragrance' from Orchids by Hausermann. I didn't expect it to be so large, and it seems to be rootbound (if thats a thing with orchids). It's in a black nursery pot, and there are so many roots I can't even tell what medium it's in. It's about two feet tall in a 4" pot.

- How am I supposed to know when it needs water? I can't put my finger in the medium, I can only feel the top surface because the roots are so thick.

-Should I repot it? It's in spike so repotting it would probably stress it out but there are so many roots in that little pot.

I am new to growing orchids but fairly experienced with other plants