Base of phal going mouldy! What can I do!

[supersheep]

I'm not having much luck with my orchids! I only bought this phal about 2 months ago and it's already starting to die on me! I'm really hoping I can save it and any help/suggestions would be much appreciated!

It had loads of lovely flowers when I bought it, but after about a month, they all shrivelled up in a matter of days and most fell off. I got a bit worried, so I repotted it with some fresh bark orchid compost. I noticed there were a good few rotten roots, so I cut these away before I repotted.

I've been very, very careful about watering it - some times it's been nearly 2 weeks before I watered it again. I've been checking the roots through the clear pot and waiting until they've gone a silvery/pale colour. And I've left it to drain after watering it.

It's been in a clear plastic pot, inside a ceramic pot, which has stones at the bottom so the orchid is never sitting in water. It lost all it's flowers a few days ago, so I cut off the flower spike above the second node up. The room its in stays around room temperature and is probably quite low in humidity, as we have the central heating on a lot at the moment. It's near a north east facing window.

Anyway, today I checked the roots, like I do every day, and they were starting to go a bit pale. But it felt very wobbly in the pot, which I thought was strange. So I moved some of the bark out of the way and saw the base of the stem was going all mouldy and looking very withered. I tipped out all the bark and saw some of the roots have gone mushy and a bit moudly now too!

I've attached some pictures and the rotting basically starts from just below the base of the bottom leaf. The leaves themselves look fine - there's 4 nice green leaves.

Now I'm wondering what I can do to save it! It has very pretty flowers, so I'm wanting to try.

I'm worried about repotting it again incase it starts rotting again and I really don't know what might have caused it. As I said, I've been very careful about watering it.

I have read hydrogen peroxide can be used for mould, but all I could get in the shops is 6% hydrogen peroxide - would this be ok and how would I use it?

Any help would be very much appreciated! Thank you!