Is “folio” an acceptable contraction of “portfolio”?
Technically, no. According to the dictionary, a folio is a single sheet, and a portfolio is a folder or case for keeping your folios. In finance, your collection of investments is called your portfolio, probably because your broker (before the digital age) would keep the records of what each of his clients held in separate portfolios.  However, I have seen the word folio used as a short colloquialism for portfolio, and if you google "investment folio" you will see it used this way, mainly in trademarked names of financial firms.