Final answer:
A macroeconomist would label Cutter's act of using his unspent income to buy stock from Phi Optics Corporation as investing, contributing to personal savings and the investment component of aggregate demand.
Step-by-step explanation:
When Cutter is spending less than his earnings and uses his surplus income to buy stock from Phi Optics Corporation, a macroeconomist would refer to Cutter's act as investing. This activity is part of personal savings, which feeds into the overall investment component of aggregate demand in Keynesian economic analysis. The expenditure on stocks increases Cutter's financial assets and contributes to the financial capital markets, where decisions about savings today affect the availability of funds for investment and thereby impact the economy's future capital and growth.