Assuming no candidate wins a majority (and that looks pretty much impossible), a run-off between the top two candidates will take place on May 7.
A banner held by a far-left protester on Wednesday read: "Far-rightists can't be fought in the ballot box".
The former president spoke by phone with Macron on Thursday morning, Kevin Lewis said in a statement.
With just a few days to go before Sunday's first round of voting, every poll for the past month has shown independent Emmanuel Macron and the National Front's Ms Marine Le Pen in the lead.
Patriots respond to comparison photo showing team with Obama versus Trump
Some players reportedly declined to attend the White House ceremony because they didn't want to be seen with Trump . In the 2015 photo, two staircases are filled with men, whereas the photo with Trump shows empty staircases.
Macron said Obama wanted to exchange views about the French presidential campaign and that the ex-president had stressed how important the relationship between the two countries was.
Macron is the only candidate so far to have said he has talked with Obama, a popular figure in France. But the race to succeed the deeply unpopular socialist President Francois Hollande has tightened in recent weeks. Some Muslims feel unfairly targeted by French laws banning headscarves in schools and full-face veils in public. Authorities announced Tuesday that they had arrested two Islamic radicals suspected of plotting a possible attack around the vote.
In the second round, Mr Macron would defeat Ms Le Pen by 64 per cent to 36 per cent, according to Opinionway, which also says Mr Fillon would defeat Ms Le Pen 58 per cent to 42 per cent.
Le Pen, who wants to withdraw France from the European Union and do away with the euro currency, defended her decision to force national news network TF1 to take down the EU flag during an interview Tuesday night. "A peaceful and democratic uprising to give France back to its people", she said, "a day of glory will arrive".