code: public function isMergeRangeValueCell()
      {
          if ($mergeRange = $this->getMergeRange()) {
              $mergeRange = Coordinate::splitRange($mergeRange);
              list($startCell) = $mergeRange[0];
              if ($this->getCoordinate() === $startCell) {
                  return true;
              }
          }
  
          return false;
      }
docs: Is this cell the master (top left cell) in a merge range (that holds the actual data value).
  
  @return bool