Phal's Second leaf turning soft.

[MrOrchidGuy]

Hello, I purchased an orchid at discount. I repotted 2 days ago and this morning I woke up and found that the second top leaf is turning soft and brown. The orchid came in an very dehydrated state but the roots were okay. Some of the roots were soft but not mushy like dead orchid roots - they still turn green when watered. The bottom leaf is droopy but not soft and firms up when watered.

I didn't soak the potting media which is very course which might mean its dehydrated. The roots were gray last night. I placed some sphagnum moss on the top to increase humidity around the top of the pot.
It has been very hot the past few days 32 degrees Celsius or around 89.6 degrees Fahrenheit.
Today is rainy and the temp is around 20 degrees Celsius or 68 degrees Farenheit.

What is wrong with the leaf, what can I do to prevent it from spreading?

Thanks!