The This Morning host were talking about the weather and how we will need to start wrapping up soon and get "warm woolly coats" out.
However Philip evidently though Holly, 37, said "willy coats" – and his reaction says it all.
He posted the clip on Twitter and said: "I just showed this to @hollywills and she had no idea. We're rofl."
The post got 11,000 likes and was retweeted more than 1,000 times.
Holly and Phil are known for their onscreen giggling fits and saucy banter.
Most recently their off camera chat was accidentally broadcasted to the entire Loose Women audience after a mic was left on during a live link.
They made a saucy "sex joke" and Phil, 56, accidentally swore before he realised one of their microphones was live.
Ruth Langsford called them out over their "rude" chat and Holly clamped a hand over her mouth in shock when it became clear that a studio full of people had heard them talking.
An audience member told The Sun Online: "Viewers at home would have been really taken aback to hear what they were talking about.
"But it was all fun and games and they were having a real hoot. No one was offended."
The saucy chat came just a day before the pair interviewed a man with a £70,000 bionic penis on the show.
It’s not the first time off-camera chatter has been picked up on the microphone from the other studio.
Most recently it was Ruth herself who was caught out when she was covering This Morning.
She was struggling to identify one of the Loose Women panelists and was heard asking Eamonn Holmes who it was,
The mysterious guest was in fact Loose Women regular Denise Van Outen.
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