It means a fear of work.
Many people experience this as a chronic ailment that blights their weekends and accounts for much of that Monday-morning feeling or post-holiday blues. It is not a new problem: the word was coined by a doctor named W D Spanton, writing in the British Medical Journal in 1905. He did so in all seriousness, recognising that it can be a real medical condition, an abnormal or persistent fear of work and the workplace.
Notwithstanding this, the word spends much of its life as the butt of heavy-handed humour, on the assumption that it is a mere synonym for laziness. An early case was an article in the Bedford Gazette, Pennsylvania, in February 1910: “The tramp is in reality a sufferer from ergophobia, or fear of work, often complicated with aquaphobia and sapophobia, which make him shun the bathtub.”
Most of its remaining appearances in books and newspapers are in lists of odd phobias, such as arachibutyrophobia for the fear that peanut butter will stick to the roof of one’s mouth.