Phal help for a newbie...root problem :(

[KatP]

New Phal owner here....

I've recently repotted my Phalaenopsis Orchid, it was purchased from a grocery store (I now know better for next time!) and when I repotted there were many roots that had gone rotten and mushy, I cut the roots that were bad and cut the stem also since it was no longer blooming and then I repotted into a medium of bark and coconut husk (soaked for a few hours).

I checked the roots today and noticed they looked withered and brown, when I took it out of the planter more roots were rotten Please help! I really like my orchid and want to take care of it. I've attached (lots) of pictures.

Thank you!!

Kat