In a tweet to actor Patrick Stewart, one of those who had parodied Cameron's photo, the premier posted a snap of a meeting with former US president Bill Clinton "this time face to face, not on the phone".
On Wednesday, Cameron posted a photograph of himself discussing the situation in Ukraine in a telephone call with Obama.
His grave expression was intended to convey the seriousness of the subject, but it was mercilessly mocked online.
US comedian Rob Delaney posted a picture of himself looking serious with a tube of toothpaste held up to his ear, writing: "@David_Cameron @BarackObama Hi guys, I'm on the line now too. Get me up to speed."
Stewart, best known for his long-starring role in "Star Trek", responded with his own photograph looking serious with a tube of wet wipes at his ear.
"@robdelaney @David_Cameron @BarackObama I'm now patched in as well. Sorry for the delay," the 73-year-old tweeted.
Cameron met with former president Clinton at his Downing Street office on Friday, and afterwards tweeted a photo.
"@SirPatStew Talking to another US President, this time face to face, not on the phone," the prime minister wrote.