How would you pronounce pheonsa?

"Pheonsa" is not a common word in any language that I am aware of. It might be a proper noun, a misspelling, or a made-up word.

If you could provide more context, such as where you encountered this word or what it might refer to, I might be able to help you with the pronunciation.

Without more information, I can only offer a general pronunciation based on how English speakers would pronounce the letters:

FAY-on-sa

However, this is just a guess. It's important to note that the actual pronunciation could be different depending on the origin and context of the word.