The codebases this is for
Core PHP with includes four levels deep, CodeIgniter 3, Yii, a custom MVC that one former employee understood. Global state, SQL built from request input, functions removed two PHP versions ago. I read it before judging it, because most of it works for reasons that are worth keeping.
Moving it forward without stopping it
Composer brought in gradually. A test around the part that handles money before anything else changes. Prepared statements replacing concatenated SQL, file by file. The PHP version raised one step at a time. The business keeps running through all of it.
When I suggest Laravel, and when I do not
If a module is being rewritten anyway, building the new one in Laravel beside the old code is often the cheaper route. A full rewrite of a system that works almost never is, and I will not pitch one to keep myself busy.