Its good old fashioned root rot whereby the media in the pot has lacked air circulation and has become to waterlogged, so therefore roots have rotted. Roots need air and light.Remove them and open up the media with chunks of charcoal or stryo/ polysterene chunks or large bark chunks.. Allow to dry betw waterings and cut some half cm wide slats in side of pot to aid airflow. This is the most common prob with orchids and phals are highly susceptable to this issue. Your plant does look reasonably hydrated and healthy. Take good care of the new roots nearest the crown/plant. Grey silver means some water please. Green means no more till i go back to silver. Brown is rottten. You will notice wirey type stringy roots under the brown decomp, Avoid moss it waterlogs easy. The bark media commonly used, deteriroates easily when wet.