If the leaves start to wrinkle your plants are way too dry. Dendrobiums prefer to dry out between waterings. Don t let them get so dry they go dormant and lose their leaves. If you mix up a weak solution, about strength, you can feed every time you water. Your plants will come home in full bloom.
Phal flowers last for months.
When the last bloom finally fades and falls off, DO NOT cut that long bloom spike. These plants frequently will send up more bloom from nodes along the spike. Only remove the spike when it turns brown and woody. New spikes will arise from the base of the plant and will sometimes look like new roots at first. Unless you have lots of space for the spikes to droop naturally, be sure to keep them securely staked.