The former Luxembourg premier told the Prime Minister he was "fully committed" to finding a solution to concerns about the EU and they discussed "how they would work together" to boost competitiveness, according to No 10.
Mr Cameron suffered defeat in his bid to stop the arch-federalist from taking the EU's top job in Brussels on Friday. A Downing Street spokesman said: "The Prime Minister congratulated Mr Juncker on running a successful campaign and securing the council nomination.
"They discussed how they would work together to make the EU more competitive and more flexible. The PM welcomed Mr Juncker's commitment of finding a fair deal for Britain and Mr Juncker said he was fully committed to finding solutions for the political concerns of the UK."