Apache Phoenix source is available on Apache Git server:
Query server repository
The source for each project can be checked out from GIT with this command (substitute the repo URL)
$ git clone https://git-wip-us.apache.org/repos/asf/phoenix.git
Each repository is mirrored on GitHub under https://github.com/apache/ , i.e.
https://git-wip-us.apache.org/repos/asf/phoenix.git is mirrored at https://github.com/apache/phoenix and so on.
Related: Using > Building
Site source access
Source for the Apache Phoenix website is kept in ASF SVN in https://svn.apache.org/repos/asf/phoenix