PHP's package manager makes it really easy to pull in components a la carte. Similar to OP, I rarely use a large framework like Symfony or Laravel. I have a base application I wrote which I like, and I layer components I trust and whose API fits my preferences as I require them.

Additionally, the PSR project has standardized a lot of APIs (HTTP request/response, logging, cache to name a few), which means if a package conforms to PSR, you get interop out of the box and can quickly swap implementations if needed.