How long have you had the plant? Did you repot it into spag? Where are you growing the plant?
I suspect overwatering, spag is good but only if watering is appropriate for that medium, also the plant looks to be overpotted and the plant should be potted so that the base of the pseudobulbs/canes is visible above the medium.
So maybe just remove a little bit off the top of the medium for now while waiting for spring and better growing conditions to arrive.
In the interim find some complete culture notes for Hardcane/Phal type dendrobiums on the net.

"one left is starting to turn yellow-ish with bumps"

What kind of bumps? Little black or brown bumps? Lots of them? Scale maybe?

Google: "scale on orchids" and check out the photos. If you have this pest, that could be another reason for leaf drop.

I am not sure of what "cut down" means in connection with hard cane dendrobium. I also don't see any evidence of scale from the pictures. Not saying Kevin is wrong but its not what is jumping out at me. I think Arthur is closest to it... it's been a long hard winter and without specialist care I would imagine an orchid would be somewhat worse for wear than not.

H

Don't cut anything down. Those bulbs are still active and help to support the plant. Agree that sphag is not good for the type of plant which may not dry out enough. Also agree the plant is overpotted, and needs a pot small enough to accommodate the roots and no bigger. Too much medium will stay too wet in the center and rot the roots. Also, dens like tight shoes, and very little nitrogen.

What's the white bubble thing in the 1st picture?

Bob