Depends on what level of macro you want, but with modern phones you can get pretty close, usually with the wide angle lens.

On iPhones: https://support.apple.com/guide/iphone/take-macro-photos-and...

On Pixel: https://store.google.com/intl/en/ideas/articles/pixel-macro-...

I'd recommend playing around with it, it's a lot of fun!

You can, depending on your definition of "useful". You can buy a cheap laser pointer, take out its lens, and put it over your camera lens. Tape it onto the lens for a temporary janky version or make a 3d-printed mount for something much better that you can easily take on/off.

I've personally found this little hack useful, but then again I don't have a DSLR and macro lens!