Your orchid is a Phalaenopsis – Moth Orchid, and it appears to have either dried out or been over-watered and suffered some root rot. How often do you water your plant? Is the orchid completely potted in bark or is there long grain sphagnum moss underneath? Potted in bark in a clay pot this Phal will probably need one good soaking per week, if it’s getting bright indirect light and normal household temps. Have added some extra information for growing below:
They have extra long bloom cycles, but when they’re done, flowers wilt and drop. During the bloom cycle, they need to be fed weekly with half strength water soluble orchid food or slow-release fertilizer formulated for blooming container plants. When flowers fall off, prune back only to green stem, since often the same flower stalk will rebloom. Check both sides of the leaves closely for mealy bugs and scale insects (the latter are like tiny scabs on the leaves). Both usually often produce sticky residue called honeydew. Remove insects with cotton swabs soaked in 70% alcohol. Does best in bright, indirect light and water every 7-10 days at the base of the plant, not in the center of the leaves. Do not allow plant to sit in water as this may lead to root rot.