it is possible to get into fin or econ phd with acct master, but no one does that.
if you want to get a job and enjoy corporate life then do acct master. If you want to be a poor phd for the next 6 years then do fin or econ phd, but fin phd has better propects than econ phd generally speaking. But again, it all depends what program you are able to get into.
econ phd has many options. you can check the job placements of some schools and get a sense where the phds end up going. finance can go to academia and industry, with most prefer to stay in academia. most of acct phds stay in academia.