First, let me say I've never made pho.
However there is already some good advice here with regards to stock:
- Should I roast meat/bones before making stock out of it?Should I roast meat/bones before making stock out of it? though I personally would also roast carrots, onion, celery with fresh herbs in with the bones.
- Should I let stock cool with the bones/veg still in it?Should I let stock cool with the bones/veg still in it?
- Are the leftovers from making stock good for anything?Are the leftovers from making stock good for anything?
What are you skimming with? I'd pour the liquid through some cheese cloth, that should at least help with appearance a bit.