You don't say how often you're watering. Paphs don't like to dry out completely, but they also don't like to stay wet. I find sphagnum moss for Paphs is very difficult for me to manage, because it stays wet for so long.
I bought one in bloom at a store a few months ago. It was in sphagnum moss. I only had to water it about once every 10-14 days. It took that long to almost dry out. My growing room is 28-30C in the daytime. In a cooler area it would take a lot longer to dry.
People use a lot of different media for Paphs, but a lot of people like small orchid bark. I don't know what is available where you live.
Your plant might have rotten roots. I would take it out of the pot and remove all the moss. Look at the roots. Paph roots are normally dark brown, which is different from other orchids. But they should be firm, not slippery or mushy, and not black. There should be no smell of rotten plant material.
I would cut off all the dead roots and repot into a better growing medium. Or, you can use sphagnum, but pay more attention to watering. You can check how moist the medium is deep inside the pot with a small wooden cooking stick. You can read about it in this thread:
Using skewers to determine when to water
Also, Paphs need very pure water with very low minerals. Most people can't use their tap water, but instead collect rain or use reverse osmosis water.
Too much or too little water? Or something else...
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