Hi André,
There is nothing specific to Phenix in that, and it also depends what you mean by "access".
If you want all accounts to have read and write permissions to a project directory: don't try that. It's a recipe for headaches at best, disasters at worst. It's really much better to require people to coordinate and communicate (which they would have to do anyway if working on the same project) than to give all permissions to everyone and hope everything will go smoothly. It won't. Files will get overwritten unexpectedly. It is generally a reasonable assumption on the part of each user that the files they create shouldn't be modified by other accounts, and giving them a system that doesn't offer this guarantee is only going to confuse everyone using it.
If you want one account to own the project directory with all other accounts able to inspect the results (but not overwrite anything!):
1) Set up a directory where these projects will go. Give it a meaningful name: I like something simple like /data. You want this on a separate partition (ideally even on a separate physical disc), because if it is on the same partition as the OS and your users fill it up with their files (as they invariably do), your system will become unstable.
2) Give all accounts all permissions to this directory: chmod 777 /data
3) Voilà! Now all accounts can create files there. With the typical default umask (see https://en.wikipedia.org/wiki/Umask ), all accounts will have read permissions to all files, but only the account owning a given file will have write permissions to that file. If this is not the case on your system, you need to either change the umask for each account to define the default permissions of newly created files (the changes will apply only to files created after it, so you would need to update permissions of all files created before that change) or define groups and use the group-level permission to achieve the same effect.
Now, I don't know how Phenix deals with a read-only project directory. You can for sure read all files with external programs. But maybe the Phenix GUI needs to write to some state files within the project even when not modifying the files being worked on; if this is the case, it will likely complain. It is easy to find out (simply try it), and harmless (since none of the project files can be overwritten if an account that didn't create them is accessing them with read-only permission).
I hope this helps,
Guillaume
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From: André Graça