Yeah I think the worst he can do is call you. I mean my insurance or company protects from others using my phone number (kinda hard to explain.) I know you can block people so you can't receive their texts or calls when they try to send them. You may want to ask your phone company though. Good luck!
It'd be terrible if someone could destroy your life just by knowing your phone number since so many people and companies have their phone numbers plastered all over their websites and business cards and posters and whatnot. Don't worry, the worst thing they can do is call you.
I think most phone companies come with blocking features. a lot of countries have the ability that if they start harassing you, then you can bring up official charges against the person via government services. there's also other things, changing numbers if they get too bad. phones cannot be hacked but people can obtain personal information via phone numbers. but just keep an eye out on your personal info like bank accounts and the likes. I'm not quite certain how they would have gotten into those unless you gave them to the person. above all else the easier thing to do would be to block, if they call again, then take it up a notch.
in the future it might be wise to use other features in order to sell items. newspapers are still used, the one you used, Craigslist, one of the bad ideas to use. there are some strange people on there and you never know they are strange until you encounter them. this is the net after all, the freaks can hide anywhere.
Just relax, there's not really anything they can do with your phone number. If there was, people's phones would be hacked all the time since it's not too hard to get hold of numbers. If it helps, keep an eye on your bank account, but I can't really see any way they'd get to that just from having your phone number.
Well done on cancelling the purchase when you did.
I know several people who actually did get scammed, so be glad that you're knowledgable enough not to fall into the trap. Just treat this as something you've learned for next time and don't be too annoyed at yourself.
Actually, I'm more annoyed at my mother. She convinced me to negotiate with the buyer anyway telling me, "At least you don't have to worry about having a gun pointed at your face." Well, that's why I meet the buyer in person at a public place that's crowded people like a cafe. Even though a gun gets pointed at my face, at least there are eye witnesses, right?