In a typical food web, organisms that get energy from producers are those that consume them. In this case, since phytoplankton are the producers, the organisms that get energy from them are:
- Zooplankton (which consume phytoplankton)
- Sperm whales (if they eat zooplankton or other organisms that consume phytoplankton)
Therefore, the primary organism that directly gets energy from producers (phytoplankton) in your food web is zooplankton. If sperm whales are feeding on zooplankton, they also indirectly get energy from producers, but the direct answer would be zooplankton.