1 - Implement code 2 - DRY (Review Code Improvements) - Do not repeat yourself 3 - Unit Test 4 - Api Documentation + PHP DocBlock 5 - Code Styling PSR-2
There is a difference between hacking and coding. For business purposes developers tended to hack which is profitable for certain situation rather small environments. However when the team grows and when the code needs to be shared, it is ineluctable that some good practice needs to be setup. Unit tests guarantee the stability of your application for every and each incremental release/deployment of your application.
Get the developers to understand that point is critical. Explaining that this practice will allow them not to be blamed after each release, they will be stress free and confident is crucial.
Obviously, this comes with more work since you now need to test your code, and write unit test, making the task more strenuous, but this is indeed HARD WORK
Documenting as well is critical especially if supporting APIs, swagger comes handy for that purpose