I raise and sell Nobile Dens.
You have a Nobile Dendrobium which is probably grown by Yamamoto in Hawaii. I deal with hundreds of his and they have certain characteristics not seen in common Nobile.
Nobles lose all their leaves every year and flower best on bare canes. Yamamoto has developed many strains (they are patented) that flower on canes with leaves. This is why I Say that you have a Yamamoto from your photo. He also has shorter thicker canes than common. His usually stay under 20 inches while others can grow straggly to 3 or more feet.
you plant is probably Sea Mary or Apollo.
Yellowing leaves are normal growth all will die and fall off. Water and fertilize heavily when they are growing, March to August and stop all fertilizer after August or they will not flower. Watering can also be reduced but I do not recommend stopping watering.
I just realized I do not have photos of the white dens. I will have to photograph them today.
But these two Yamamoto Dens show how they are shorter thicker canes (very thin at the bottom) and flower from canes with leaves.
these two Dens are more normal and flower from the leafless canes and grow scraggly (but pretty) The first is Den Second Love
