Final answer:
A virus acquires its envelope during the maturation phase, using the host cell's membrane structures.
Step-by-step explanation:
A virus obtains its envelope during the maturation phase of its life cycle. This envelope is derived from the host cell's membrane structures as the virus assembles and prepares to exit the host cell. New viruses are assembled using the viral DNA and proteins produced by the host cell, and during the release, some viruses take a portion of the host cell membrane to form an envelope around the capsid.