why does lenina feel that epsilons should provide less lhosphorus after their cremation

Lenina and Henry Foster finish their game and go to his apartment building. On the way, they see a cremation factory, which leads them to discuss the physic-chemical equality of all caste members, from Alpha to Epsilon. She feels that being a lower caste meant they had less Phosphorous to give but maintains that, "even Epsilons perform indispensable services."