Orchid Questions From A Beginner

Hello there,

Recently I bought 3 orchid plants. 1.Phalaenopsis. 2.Dendrodium and 3.Zygopetalum. They are beautiful.

However, the leaves of the Zygopetalum turn yellowing and black. I cut those leaves that rotten. I was wondering whats the real problem is with this orchid.

The Phals. and the Dendrodium seems relatively okay at the moment. Should I take them out from the plastic pot and transfer into more aerated-spaces pot? I dont want them to die. Especially the Zygopetalum.

Please advise.