Best potting medium for Mini Phal?

[Emerald27]

I have a Mini Phal with about a 5 inch leaf span that I repotted a couple months ago in a mixture of coconut husk, perlite and lava rock. It was originally potted in sphag moss. Since repotting, many of the visible roots have gone all brown, wirey and dry. I saw a new root starting to emerge a few days ago, nice and green, then checked for it yesterday and it had already shriveled and turned brown. The leaves are still healthy looking, but the roots are worrying me. I think that perhaps I don't have the orchid nestled into the medium enough, and maybe this is causing so many dried out roots. Should I try to get the base of the orchid deeper into the medium, might this solve the problem?

I read in an article that large Phals do well in bark or husk mixtures like the one I'm using, but that smaller Phals do better in spagh. Was it a mistake to repot this Mini Phal out of spagh and into a coco husk mixture? Should I transfer it back into sphag?

Thanks in advance for any feedback!