Phalaenopsis with black spots on roots

[ss12334321]

Hi! This is my first time of taking care of an orchid. I got a phalaenopsis because they are so beautiful. I read that some people recommend that you repot it immediately after buying so that you can asses if the orchid has root rots. When I repotted it, there was only one root that was mushy so I cut it out. The other roots where plump and firm. However the plump and firm roots were not green they are yellowish white with some small black spots on them. Are these roots healthy of are they about to rot? Should I cut them of as well? Also, do I need to soak the roots in fungicide after trimming of a section with root rot? Thanks.