Overgrown dendrobium keiki?

[Misa]

Hi,

I bought this orchid at a plant sale at my local botanical gardens, they said most of their plants were donations from members. I'm thinking it's a dendrobium but it hasn't done much since I got it. Am thinking of repotting it soon since it's so small for the pot that its curgently in. The bottom part used to be green but now it's yellowed. I guess I'd like to know what it is so I can proceed appropriately. Thanks in advance!