License
PhlatPage is AGPL-3.0-only, with an additional permission that keeps your own site code out of the covered work.
On this page
PhlatPage is licensed under the GNU Affero General Public License, version 3 (AGPL-3.0-only), with an additional permission under section 7. The full texts ship with the framework as LICENSE and LICENSE-EXCEPTION.
Your site is yours
The code, templates, fields, fieldtypes, addons, configuration, content and assets that make up a site you build on PhlatPage are not covered work under the AGPL, as long as they contain no part of phlat/. That is everything in:
site/data/- any addon outside
phlat/
You may license these on any terms, keep them private, and run or distribute them together with PhlatPage. Section 13 does not require you to offer their source to your site's visitors.
PhlatPage itself
Everything in phlat/, including its built-in addons, stays under the AGPL. If you modify it and run the modified version on a server, section 13 applies as usual: offer its source to the users who interact with it. A file copied out of phlat/ into your site keeps its license. An override that starts as a copy of a shipped file is AGPL. One that composes, by including the original or overriding at a seam, is yours.
Removing the permission
As section 7 allows, you may remove the additional permission from your own copy of PhlatPage. That copy is then plain AGPL-3.0.
History
Before v0.9.3, PhlatPage was GPL-3.0. See v0.9.3.