Which phrase refers to the inherent power of the state to protect persons legally incapable of protecting themselves?

Parens Patriae

Explanation:

Parens patriae is a legal term that describes to the power of the government to act in the interests of individuals who can not provide for themselves.

For instance, parens patriae doctrine empowers a judge to grant or reallocate a minor child's custody, irrespective of the wishes of the parents.

In fact, parens patriae can be interpreted as specifically as serving a single child's interests and as widely as ensuring the entire population's well-being.