Former prime ministers' numbers were among those visible on a government website for more than three months, Fairfax Media reported.
The details appeared invisible until they were highlighted with a cursor or copied and pasted elsewhere.
PM Malcolm Turnbull and some leading members of the government were not affected.
But Fairfax said the bungle hit Opposition Leader Bill Shorten, and former prime ministers Julia Gillard, John Howard and Paul Keating.
The information has since been removed from the Department of Parliamentary Services (DPS) website.
In a statement to the BBC, the department said the numbers were included on a report into parliamentary phone and data spending.
The report was created by private contractor TELCO Management, the statement said.
"In the most recent report provided by the contractor, it became possible to view the official mobile phone number of parliamentarians and their staff even though they appeared redacted from the published files," a DPS spokesperson said.
"The DPS removed the documents... shortly after it was alerted to the issue and is working with the contractor to investigate the cause."
The department would address privacy concerns with MPs, said the spokesperson.
The number of those affected was not revealed, but Fairfax said it ran into the hundreds.
TELCO Management has been contacted for comment.
The private phone numbers of a large section of Australian politicians have been mistakenly published online.