We don't have any specific integration with Phoca Download, but you can probably use By URL Part protection to protect access to the download URLs or if Phoca Download has ACL you'd just give users usergroups based off their subscription (see Access tab of your plans).

You can also look into using our download manager CB Package Builder, which integrates with CBSubs. It's primarily used for Joomla package building, but doesn't have to be as you can use Document or Custom package types to avoid the Joomla packaging behavior and use it like a regular download manager.

The Joomla packaging is ignored for Custom types. It's how we offer our manuals for download. If there are no Joomla packages available it should hide all of the Joomla related functionality (e.g. check all, Joomla version dropdown, and download button at bottom). At any rate if you still want to use Phoca Download it should work fine either by using ACL or By URL Part protection.