Restraint and moderation. The Phantom demonstrates this by not being driven by vengeance or revenge even when he suffers great personal loss.
The Phantom uses violence to resolve conflict, but remains merciful in the face of victory, exercises discretion with his use of force and never kills. Where there have been exceptions to this and The Phantom has been driven by vengeance (Death of Diana, the First Phantom seeking out his father’s murdered (The Avenger), The Phantom’s who have done this have shown restraint, mercy or compassion at the last safe moment).
This is illustrated in the story ‘The Chain’ where The Phantom is imprisoned while rescuing his future wife and sentenced to hard labour chained to a stone mill. Initially filled with a thirst for vengeance, and then desperation, he notices that with each turn he is slowly wearing the chain. With renewed hope he focuses on this, breaks the chain, rescues his wife and restores balance to the universe. But he takes the chain and places it on the Skull Throne as a totem, a symbol to demonstrate resilience, patience and persistence.
In its simplest form, his temperance is embodied by The Phantom’s abstinence from alcohol and drugs to the extreme of ordering milk in a seedy bar filled with roughnecks.