You can block ambient noise in a Facetime call by opening Control Center during a Facetime call, tapping Mic Mode, and selecting Voice Isolation.
How to Block ambient noise in a Facetime call
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Ambient sounds for working (or sleep)
If you like ambient sounds for working (or sleep), you can turn that on your iPhone by opening the Control Center, tap on the ear, and click on background noise.
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10 iPhone Tips and Tricks for Screenshots, FaceTime, and More
Useful iPhone tips including screen recording shortcuts, screenshot editing, keyboard tricks, and ambient sounds