Yes, it looks like the planting medium is breaking down, so time for a repot. Get a bag of fir bark chunks, soak in water overnight. You can probably reuse the pot it is in now, if there is good drainage with it. With your fresh bark soaked, carefully remove this phal from its pot and remove the old medium from the roots. Soaking the roots in tepid/room temp water for 10 or 15 minutes will help you figure out which roots are live. The live ones will be plump and firm after soaking. Any that are black are rotted, any that are soft/squishy are rotting and need to be removed before repotting. After cutting off the rotted or broken roots, I like to soak again, this time in Hydrogen Peroxide for 10 minutes or so. Then you are ready to carefully pack new bark around the roots and secure your phal in its pot. You may want to pull it back from the south window far enough that it does NOT get any direct sun, maybe just off to the side where the light remains bright.