It is normal for the flowers to die back after a month or two. You were right to cut back the flower spike. However, it is not normal for leaves to be dying on your Phalaenopsis.
The plant appears to be potted in very large bark chips. That is fine, but the larger chips do not retain water very well so the Orchid usually needs more frequent watering. You didn't mention your watering routine, but my educated guess is that you are losing leaves because the roots are not getting adequate water.
Once or twice per week, take the inner plastic pot to the sink and let warmish water flow through the bark chips for a minute or so. Of course, there has to drain holes in that pot for the excess water to flow through. Never let the inner pot sit in water that has collected in the bottom of the outer pot.
A sunny north window is best.
