Freedom towards, not freedom from
Frankl did not claim that a person is free from biology, psyche or social conditions. He claimed that they are free towards them - they can take a stand and decide who they will become. A human being is not fully conditioned and determined; it is they who decide whether to give in to conditions or stand up to them.
Against “pan-determinism”
Frankl criticised pan-determinism - the view that a person is merely the product of genes, drives and environment. He considered it dangerous because it takes away people's responsibility.
Freedom and responsibility
Freedom without responsibility degenerates into arbitrariness. Hence Frankl's famous remark in a Harvard lecture (1961): the Statue of Liberty on the East Coast of the USA should be supplemented by a Statue of Responsibility on the West Coast.
The defiant power of the spirit
This freedom shows itself in the defiant power of the spirit - the human capacity to stand up even to one's own weaknesses, fears and illness.
Sources
V. E. Frankl, Man's Search for Meaning; Viktor Frankl Institut Wien - biography (1961).