1. Weight and Size
The average phone weighs 6 oz, while the average camera weighs roughly 2 lbs (32 oz) without a lens. Phones are also designed to fit in your pocket, whereas the vast majority of cameras wouldn't be able to.
2. Auto Features
While most cameras can shoot with the camera choosing all your settings, the majority of phones make it even easier by being set to automatic by default and shooting and editing HDR photos automatically. Plus phones have internet access and apps, allowing them to be able to take photos and instantly be able to upload them to the MLS or social media.
3. Cost
Cameras are expensive, and most of them don't come with lenses, which are also equally, sometimes more, expensive, whereas phones already have at least one lens attached. Most modern phones also include more lenses, which adds to their usefulness. Also, you more than likely already own a phone, but not a camera.
On top of all these advantages, phones have another secret advantage: they shoot with a taller aspect ratio. As shown on the right, the black bars on the top and bottom are the additional information seen by your average phone camera over your average camera. This is because the sensor has a different aspect ratio, allowing it to capture a bit more vertical info. This is great for real estate photography because you can get more information in the same photo without having to step back or reframe the photo.
However, this advantage is mitigated by the versatility of professional cameras with interchangeable lenses because you can just attach a slightly wider lens to the camera and get the same information vertically and more horizontally. But usually, the wider a lens is, the more expensive it gets; so this is still an advantage for your phone, unless you are willing to spend more to get a wider lens for your camera.

While phones have quite a few advantages, they are still outnumbered by the disadvantages. Cameras have a sensor that is almost 30x larger than the average phone sensor. This allows them to take photos in darker scenarios while still retaining detail, gives their photos a shallower depth of field (blurrier background), and allows them to create higher quality images because the sensor has room for more, larger pixels. Cameras also have a bunch of ports and connection points on them, allowing them to be mounted to tripods and stands, connect to monitors and triggers, and attach flashes and transmitters to them. Plus, there are a lot of (very expensive) professional lenses that allow you to take very sharp photos at whatever zoom you prefer. They can also shoot photos at a faster rate and higher quality video, with the ability to flip out the screen and view the live feed from your camera at basically any angle.
Below is a visual comparison of a phone photo and the same photo but taken with a camera.

This photo was taken on an iPhone 15 Pro; this was shot as a RAW photo and slightly edited to increase sharpness and brightness.

This is the same iPhone Photo (Left) compared to the camera photo (Canon EOS R5C) (Right). The camera photo has been edited and is downscaled to 10 mb to fit in the ARMLS's restrictions, whereas the iPhone photo, with edits, is 52mb.

These are the same photos, but zoomed in more to further show the difference in sharpness.
As you can clearly see, the phone photo, while easier to shoot and share, is clearly much less detailed. This is primarily because the phone's sensor is tiny, causing it to take very noisy images. The phone then corrects the noise to make it easier to look at, which causes the splotchy look that most phone photos have. This can be mitigated by either adding more light to the scene or using a longer exposure. On most phones, you can use third-party apps to control your camera further. The only issue with that is you'll need to use a tripod or something to steady the photo; otherwise, it'll become a blurry mess.
Photos taken on a phone are obviously not going to be better than on a camera. However, phone cameras are getting much better, allowing them to be used more and more in real estate. You don't get professional levels of detail with a phone camera, but in a pinch, they definitely hold their own. Plus, having phone photos for your listings is infinitely better than not having any photos.
As Chase Jarvis said, "The best camera is the one you have with you."