In her Instagram Story on Tuesday, the American Idol alum, 37, shared a screenshot of a text conversation between herself and Foster, 71, after she had sent him a behind-the-scenes picture from her photoshoot with intimates brand MINDD.
"I'm an underwear model now," McPhee texted Foster alongside the snapshot, prompting the music producer to reply, "Vava vavA-voom."
"Hot mom," Foster, who shares 6-month-old son Rennie David with McPhee, continued in his text. "I tried u a bit ago but u are obviously busy stripping!! 😂 U look amazing!!! Wow!!!"
McPhee quipped in her response: "Stripping indeed 🤣."
The Smash star posted another picture from the shoot on her Instagram Wednesday, joking in the caption that she was now "looking for the GenZ affirmations."
"i know i know… this screams 'look at me!' but really will you?" she wrote.
Charley Gallay/Getty David Foster and Katharine McPhee
The comments section were flooded with responses, with Lindsey Vonn writing back, "Crushing!! 💪🏻💪🏻🔥🔥."
Earlier this month, Foster raved about McPhee on Instagram when the "Over It" singer shared a series of photos from a family trip to Canada.
In one of the pictures, McPhee was seen holding her son Rennie as she waved at the camera from a trail in a sunny garden. Another shot showed the mom of one giving her baby boy a big smooch on the cheek in front of a body of water.
"HOT MOM!!!!! 🔥 " Foster commented on the post.
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McPhee has been feeling comfortable with her post-baby body since welcoming Rennie in February, she previously told PEOPLE.
"I thought I would have this pressure [to bounce back] but I've just been so grateful and happy that I've had a healthy baby and I've felt really good, emotionally and physically," she said this March. "I'm so happy that I don't have this crazy pressure yet to fit into whatever jeans I have in my closet."