Final answer:
The phrase that embodies the theme of disease and decay in Act IV, scene VII of Hamlet is "It warms the very sickness in my heart", spoken by Laertes, reflecting the moral and psychological corruption in the play.
Step-by-step explanation:
In the excerpt from Act IV, scene VII, of Hamlet, the phrase that supports the theme of disease, rotting, and decay is "It warms the very sickness in my heart". This line is spoken by Laertes and metaphorically refers to the festering of his desire for revenge, which can also be interpreted as a reflection of the moral decay and corruption permeating the court of Denmark. Themes of disease and decay are prevalent throughout the play, often symbolizing the deteriorating state of the kingdom under Claudius's rule and the psychological distress of the characters.