You water only once every 10 days? That actually sounds a bit like under watering, yet the roots you show were clearly rotted from over watering.
I suspect that the sphagnum moss in the pot was packed in really dense and that it held in the water all too well. It also probably suffocated the roots.
If you go to an all bark mixture, be prepared to water more frequently. The bark can dry out in a matter of just a couple of days, even bone dry if the plant is by an open window.
I've made two classic mistakes with phals that I'm hoping you can avoid. The first is not changing the potting medium after the first year. It's essential to do this because most of the time the moss breaks down by then, becoming too mushy and acidic for the plant. The second is over watering. If you go by the surface of the moss, you will be tempted to water the plant when the top is dry but the bottom moss is moist. The moss around the roots won't get a chance to dry out. This also promotes fungus.
The insidious thing is that when the roots start to rot, the plant begins to look like it's not getting enough water, so you add water more frequently... which enhances the root rot!
When you've got a bad root system, bark can be a tricky thing to use. There's not a lot of root available to help keep the plant in position. It might be better to start with some bark in the base and fill the rest with moss.