First of all, there is good news, you have some small, but healthy looking growths there. If I see this correctly, there is even a tiny new growth starting.
I wouldn't worry about the yellowing leaf. Most of these type of Dendrobiums leaf out during their growing season, then drop their leaves and bloom most of the time on bare canes.
Now the bad news is
that pot is way too big and there is simply too much bark. These Dendrobiums like to be pot bound/ walk out of the pot to do well. (I have a similar plant, I have been growing it without medium for years) Also, if any way possible, give it as much light as it can take without burning. ( at least here in NJ! )
The bare cane will not leaf out again, but it is still functional.