code: public function buildReducePhase($bucket = '', $key = '', $source = '', $language = 'javascript', $keep = true)
      {
          $this->setPhase('reduce', $this->assemblePhaseData($bucket, $key, $source, $language), $keep);
  
          return $this;
      }
docs: buildReducePhase
  
  Allows you to define the Reduce Query Phase by using parameters
  
  @param string $bucket
  @param string $key
  @param string $source
  @param string $language
  @param bool $keep
  
  @return $this