The application deadline for DPhil students at the Department of Zoology at Oxford is in January. Check out information about this program here. Please contact me well ahead of the January deadline (~October of the year before you want to apply) with the following information:
The questions or hypotheses that you would like to test during your DPhil
The study system(s) you would like to use and why
The funding bodies that you are eligible for and are pertinent to the proposed research
Your CV and any pertinent publications
Funding to do your DPhil at Oxford can be obtained through various internal/external fellowships. Note that to be eligible for much of the internal support you must be a UK or EU citizen - with the exception of funds like Natural Motion or Clarendon. Other funds that are worth exploring include the Rhodes Foundation, or scholarships from your own Institution/State/Country.
To understand what external funding options may be open to you, I recommend you contact the graduate office at your undergraduate university, chat with any personal contacts from your country who might have come to Oxford, or even your embassy/consulate. Private foundations can also offer fantastic sources of support for DPhil tuition and more, but these are not very well advertised, so may require some investigation.
The following website explains the various ways to come to carry out your DPhil at Oxford Zoology.
Also, check out available funding opportunities in this document.
Note that fellowships are very competitive - your chances will be materially approved if you have (at least) one peer-reviewed publication already.