Mr Obama gave “a lot of stuff” to African Americans, Hispanics and young voters – groups key to his victory, Mr Romney told donors on Wednesday.
Mr Romney’s comments were his first since his election concession speech.
He lost the 6 November election by a wider margin than many expected, failing to win key swing states.
Mr Obama secured re-election with 332 electoral votes to Mr Romney’s 206, with battlegrounds including Ohio, Virginia and Florida all falling to the president.
‘Troubled by the past’
Mr Romney’s remarks come as Republican state governors gather in Las Vegas, Nevada, to discuss the party’s route forward.
“The Obama campaign was following the old playbook of giving a lot of stuff to groups that they hoped they would get to vote for them… specifically the African-American community, the Hispanic community and young people,” Mr Romney is reported to have said.
The former Massachusetts governor noted that Mr Obama’s 2010 Affordable Care Act was a “huge plus” for some voting groups.
“With regards to African-American voters, ‘Obamacare’ was a huge plus – and was highly motivational,” he said in the call.
“You can imagine for somebody making $25, or $30, or $35,000 [£22,000] a year, being told you’re now going to get free healthcare, particularly if you don’t have it, getting free healthcare worth, what, $10,000 a family, in perpetuity, I mean this is huge,” he added.
Mr Romney also noted that allowing people under 26 years old to stay on their parents’ insurance plans had been very popular with young people, and offering what he called an “amnesty” to the children of illegal immigrants appealed to Hispanic voters.
In accounting for his loss, Mr Romney downplayed any shortcomings of his own campaign. He described his operation as a “very solid team that got along”, adding it “did not get in the way”.
The Los Angeles Times newspaper reported that the former presidential candidate did not seem to be aware of journalists listening to the call.
Mr Romney told supporters it was difficult to think about what he would do next.
“We’re still so troubled by the past,” he said, “it’s hard to put together our plans for the future.”
Meanwhile, Republican governors who were meeting in Las Vegas, Nevada, said their party needed to learn lessons before the next presidential election in 2016.
Louisiana Governor Bobby Jindal said Republicans needed to accept “we got beat”, and several Republicans said the party could lose again if it doesn’t change its strategy.
Describing Mr Romney’s analysis as “absolutely wrong”, he told Politico: “We have got to stop dividing the American voters. We need to go after 100% of the votes, not 53%. We need to go after every single vote.
Former Mississippi Governor Haley Barbour said: “We need to have a brutal, brutally honest assessment of everything we did… and determine what we did that worked and what we did that didn’t work.”