A project with a cool team and architectural solutions really needs a web developer to participate in the creation of a high-load site and platform.
One or more PHP frameworks (laravel, symfony, yii, etc.);
Basics of working with a database - working with complex queries, working with indexes, profiling queries ⁃ understanding how caching works (Redis, Memcache, couchbase or mongoDB are suitable);
An understanding of design patterns and the ability to apply them where necessary.