I don't give my phone number when I first reply to an ad. I do however make my response more than a one liner, and do give my location and suggest a local meeting place for inspection by name. I also look at the email address of the person that replied when I'm selling something. It's safe to say that business domains, and .edu addresses are legit, at least that's been my experience. Most of the trash comes from yahoo and gmail emails..... another reason I give a lot of info when I reply to an ad using a gmail email.
I also use a gmail account for anything CL related. Easy to dump and create a new one if needed. So far it seems as though the spammers don't even add gmail emails to their lists, as I've never gotten any junk even after taunting the spammers/scammers.