PHP interviews cover language semantics, OOP, Laravel or Symfony, MySQL, and web security basics. Below are the most common questions with model answers. Senior: architecture, trade-offs, mentoring, and decision-making.
Not in the controller and not in the model, because the first makes it unreachable from a command and the second makes the model a place everything accumulates. Service or action classes with a single responsibility, taking what they need and returning a result, stay testable and callable from a controller, a job or a console command alike.
In stages that each work with the running code: add a nullable column, deploy code that writes both, backfill in chunks, switch reads, then remove the old column in a later release. The specific PHP trap is opcache — a deploy that swaps files under a running process can serve a mix of old and new until it is cleared.
A profiler over a real request rather than a guess — Xdebug or Blackfire will name the function, and the answer is usually query count rather than PHP itself. Then check the obvious infrastructure: opcache enabled in production, and whether the framework is booting more service providers than the request needs.
Cache the expensive and stable: a computed report, a config tree, a query whose result changes rarely. Tag it so a related write can clear a group rather than the whole store. Time-based expiry is wrong but self-healing, and for most read-heavy data it beats explicit invalidation you will eventually forget to call.
By staying close to the framework rather than wrapping it in your own abstractions, since every wrapper is something you maintain across their upgrades. Then: a dependency policy, static analysis at a level you actually enforce, and upgrading one minor version at a time so the jump is never a project. A codebase two majors behind is one nobody wants to touch.
For a small service with one job, where the boot cost and the dependency surface buy nothing — a few files and a router are honest. The moment you need auth, migrations, queues and a permission model, writing them yourself costs more than learning someone else's. The decision to be wary of is a framework chosen for a service that will never grow into it.
In a real interview you speak under pressure. Cam asks these same questions, scores every answer, and shows exactly what to fix.
Practice a Senior PHP Backend interview →