I got a new number recently.
One of the first calls I received was a debt collector looking for the previous owner. They were not the last collector to call me. I now know his name is Alvin ___ and he has some outstanding debt. Being debt collectors, I probably could have pretended to be a roommate or AA sponsor and pressed them harder to get more details about the guy.
One of the next calls I got was from CVS pharmacy, telling me Alvin's prescription was ready to be picked up. CVS requires you to validate some other piece of information before they'll tell you the name of it, but other pharmacies might reveal more about your prescriptions without additional verification.
I also got a call from his doctor. They left a message requesting he call back about his test results. I didn't follow up.
I received a string of group text messages from his co-workers about sports games, delivery plans and pickup locations and got berated by one of them for not showing up to a job. After being sent a picture of a barrel "I" had failed to pick up, I learned Alvin works in hazardous chemical delivery. So now we know he's a blue-collar guy and likes sports. That should help limit the password pool. His co-workers likely could have yielded more information such as email or residential address.
I also received a 2FA message intended for Alvin. Now I know where he does his banking. All I need is an email address...
Eventually traffic destined for Alvin came to a stop.
Then I signed up for a Google Voice number. I immediately got a text message intended for the previous owner soliciting sexual favors for an insultingly low amount of money. I politely declined his offer.
Long story short, there's a lot you can learn about an individual when you have their phone number.