captive
俘 centers on a person taken and held against their will: a captive or prisoner of war.
俘 combines 亻 (person) with 孚, which likely contributes the sound and may relate to capturing or seizing. The exact historical development is uncertain.
A person 亻 is held by a claw 爪 over a child 子, like a captive being restrained. The right side 孚 suggests a grip that traps the person.
For フ, imagine a captive being led away while someone says "Foo!" in a dismissive tone: foo -> フ, and the captive is taken.