Totally agree with everybody here. And definitely agree that from that particular photo, not enough watering.
Make sure to know that dry bark repels water. Very dry bark takes some amount of water soaking before water can get into it. So if watering very bark - the water could simply just slip off the surface and the orchid roots can dry right up....and the leaves will dry up.
But ---- at the same time, make sure to avoid making the media overly wet all or most of the time.
And refer to these tips:
Click Here and
Click Here