Have you had much luck with slots? I have a project using View Components that leverages slots. I've tried migrating to Phlex, but the lack of explicit slot support has been a bit frustrating.
Slots are pretty easy in Phlex. Have a look at the README in the repo I linked for an idea. I just create `with_column` or `with_header` methods that take a block and store it.
To create them declaratively (not needing to call them in a set order) you just create a module that defines `before_template` and calls `vanish`: https://www.phlex.fun/miscellaneous/v2-upgrade.html#removed-...