The Sun can also reveal they joked about who had pinched their shared “build back better” slogan from who and bonded over their mutual love of trains.
The PM beat his fellow European leaders to the first call with the new White House chief.
The pair, who have never met, spent nearly 40 minutes getting to know each other on Saturday night.
Mr Biden, who some have suggested harboured a dislike of Mr Johnson because of Brexit, is understood to have reaffirmed that the UK is “the US’s closest ally”.
The PM pointed out that a million Americans work for British firms across the pond, and a million Brits work for US firms UK as the reality of that bond.
When Mr Johnson won his massive election victory in 2019, Mr Biden publicly called the PM a “clone” of Donald Trump.
But Downing Street said yesterday the call was “warm and friendly”.
However on a darker note they both agreed climate change posed an “existential threat” to our way of life.
And they vowed to put green issues at the top of their shared agenda ahead of the UK hosting the major COP21 climate summit in November that Mr Biden is likely to attend. He is also expected in Britain in the summer for the G7.
But No10 left the door open to Mr Johnson jetting to Washington before then to meet the new US President, saying: “The leaders looked forward to meeting in person as soon as the circumstances allow.“