Hi @lichenzhang04,
Thank you for your question about caring for orchid seedlings and welcome to the Bunnings Workshop community, it is fantastic to have you with us.
The "sponge-like material" is likely similar to these Jiffy Coir Pellets, which are a great growing medium that nurseries often use to propagate seedlings.
I would suggest removing the coir and filling a pot with Scotts Osmocote Orchid Premium Potting Mix before repotting the orchid. Orchids like a snug pot, so something around 5cm bigger in diameter than its current pot is ideal.
The potting mix contains enough slow-release fertilizer to feed the orchids for 12 months, so there is no need for any additional fertiliser at this stage.
They like light, but direct sunlight can burn the leaves, so they should be placed in an area with bright indirect light such as an east-facing window.
In terms of watering, they should be kept moist, but not sodden. Check the top 2-4cm of soil before watering. During the seedling stage, you should be checking the soil every 2-4 days. If the soil is still moist, wait a day or two and check again, if the soil is dry, then water your orchids.
You might like to check out How To Plant, Grow And Prune An Orchid and How To Grow A Phalaenopsis Orchid for some further guidance.
Also, allow me to tag @Noelle, our resident horticultural expert to see if she has any other tips.
Let me know if you require any further assistance.
Jacob
