Final answer:
The building phase of metabolism is referred to as anabolism, which involves the synthesis of complex molecules from simpler ones, consuming energy in the process.
Step-by-step explanation:
The building phase of metabolism is called anabolism. Metabolism is composed of both building (anabolism) and degradation (catabolism) pathways. Anabolic reactions are essentially building reactions that consume energy to create complex molecules from simpler ones, which are necessary for the growth and maintenance of an organism's cells. In contrast, catabolic reactions break down complex molecules into simpler molecules, releasing energy that can be used for various cellular processes, including fueling anabolic pathways.