There are instances when the phrases are useful. Like “people with uteri should get a pap smear every few years”, in that case you’re simply using it to talk about a relevant body part without gendering the people who own it.
In other cases, the phrase is misused, like “people with penises just don’t understand the shame people with vaginas feel about their genitals”. In this case, it carelessly throws cis men and trans women together as if their experiences are identical, even though trans women are very familiar with genital shaming. This kind of carelessness is often a result of the way society drills into our minds that trans women are really men, which influences our thoughts and words.
Even when just talking about bodies, think before you speak and try not to make assumptions. For example I remember a post about heart attacks that said that “people with vaginas experience different signs when having a heart attack than people with penises”. The poster probably felt real proud of being such a great ally after using these phrases that they heard somewhere, but have there been studies on what causes these differences? Would a trans woman experience different signs before and after bottom surgery due to suddenly having a vagina? Or is it hormonally caused so hormone replacement therapy would alter the signs? The answer is we have no idea because these things are all made for cis people, by cis people. So best not to make any assumptions: “cisgender women tend to experience different signs when having a heart attack than cisgender men” you can leave it there, or add “there is no data about this on transgender people”.
The phrase is not always wrong, but -think- before you use it. Understand that society has programmed you to assume that trans men are like cis women, and that trans women are like cis men, understand how that influences your thoughts and words. Understand that body parts and hormone levels are not immutable, and that body parts don’t always come in one of two complete packages(example: having a vagina does not automatically mean a person has a uterus). Basically, just -think-. You won’t always get it perfect, and that’s okay because the way our culture has built language around sex and gender makes it extremely hard to speak about these constructs without reinforcing them, but the attempt is appreciated.
Wow, this reply got a bit long. Anyway I hope this helped and have a nice day!