Dr Phelps maintained while campaigning for the eastern suburbs electorate of Wentworth that she intended to hold onto her position with the City of Sydney council.

But she remained tight-lipped on Tuesday as she held her lead over the Liberals' Dave Sharma and amid questions over her eligibility - and ability - to represent two constituencies at the same time.

Her wife, Jackie Stricker-Phelps, said Dr Phelps was "spending the day thanking volunteers" and would comment once the final votes had been counted.

Former federal MP Philip Ruddock, who was elected Hornsby mayor after decades as a Howard government minister, spoke to Dr Phelps about the demands of each role on Monday night.

"Very frankly, it depends on how you want to do the job," Cr Ruddock told the Herald.

"If you are going to do the job properly, there are exceedingly heavy demands; the demands are insatiable."

Cr Ruddock said voters expected to see their federal member at weekend events and 12 to 15-hour working days were typical. "That said, not everyone does it.

"If you're conscientious and you respond to every request, you don't have a spare waking minute."

Queries over Dr Phelps' eligibility have swirled around whether her council role and job as a practising GP are at odds with section 44 of the Constitution.

Specifically, whether she holds an "office of profit" under the Crown that would make her ineligible to sit in federal parliament.

Dr Phelps has refused to release legal advice she sought from barristers Geoffrey Kennet SC and Perry Herzfeld, but said in a statement:

"I am confident on the basis of my own knowledge of the relevant laws and information available to me that I have no section 44 issue whatsoever."

Constitutional law expert Graeme Orr said section 44 "doesn't touch local councillors" .

"But it has been years since anyone thought they could juggle two such high-profile jobs," he said.

The High Court found in February that former Devonport mayor Steve Martin was eligible to replace Tasmanian senator Jacqui Lambie.

A second constitutional law expert, Anne Twomey, said Dr Phelps' legal advisers would have applied principles from the Tasmanian precedent to the relevant NSW law concerning the City of Sydney.

"Assuming that both laws treat issues such as remuneration and removal from office in a similar way, she would be OK."

Professor Orr said he would only expect Dr Phelps to resign from the council, before her term finished in 2021, if she was re-elected in Wentworth.

"At the 2019 national election, it may be politically wise for her to campaign on a pledge to give her sole attention to the Canberra role. That would give her a solid reason to leave the council early."

Perhaps she wouldn't make that decision and "hedge her bets", Professor Orr said.

"Is she a superwoman? Is there enough overlap in the geography of her constituency roles?

"And if Labor enters the election likely to gain a majority she may feel that being re-elected to Canberra won’t be so demanding."

Professor Orr also said it was "very, very unlikely" Dr Phelps would fall foul of the eligibility requirements because she was a GP who received Medicare rebates from the government.

Dr Phelps was elected to council as the first on the ticket of Cr Moore's group of independents in 2016 and had served as deputy mayor until she dramatically quit that team last June.

A City of Sydney council spokeswoman said there were no restrictions on its councillors also serving as federal parliamentarians.

The ban on state MPs sitting on local councils triggered lord mayor Clover Moore's resignation in 2012 from NSW Parliament, under the O'Farrell government's so-called "get Clover" laws.

Cr Moore gave high-profile backing to independent candidate for Wentworth, Licia Heath, in a move that had been predicted to lure votes from Dr Phelps.

The City of Sydney will hold its next full council meeting next Monday night.