Phone cam spying can happen but not as effective. We tend to hold our phones closer to us to view the screen (for long periods of time) and the rear facing camera is mostly pointing downwards. When we put our phones down it’s usually flat on a seat/table pointing to the ceiling or black in our pockets or bags. Webcams on laptops or desktops tend to be left more horizontal and at a desk facing into the room it’s in. So if those are in bedrooms or dorms and that’s where you change, then definitely cover up the lens when not in use!
It’s easier for hackers to try and find compromising pictures or video that already exist, and I’m sure there are plenty of those with the changing behaviour of the smartphone generation. The iCloud hack of celebrities a few years ago springs to mind, you’d think being celebrities they’d take the steps to delete the compromising pictures after whatever reason or whoever they took them for to begin with ( with the inherent weakness of the recipient should have the only copy and how secure is the recipient!)
Scams involving compromising pictures or videos that they don’t have are rare, most people would demand to see evidence first. If they do prove to have the pictures or videos, then it’s blackmail rather than a scam. Trouble is the victim is trusting a blackmailer to play fair and not expose the items. Once they pay the first time the blackmailers always return because they know you were desperate enough to pay and they have that power over you.