Rest API (PHP/ JSON/ XML)

I'm looking for someone to build a Rest API (using PHP/ JSON/ XML), on which multiple web services can be build.

The project will be done in multiple phases.

Phase 1: Build core API (secure)

Phase 2: Tweak the core API and extend the basic functionality

Phase 3: Extend the API with additional functionalities

Phase 4: Further extend the API with additional features