If you insist on a phone number in the ad, you are losing buyers. I would have to want something *really* bad to send you my phone number immediately. I don't want to send you my phone number until we've exchanged a couple emails and I know you're not a psycho. When we're arranging pickup, that's when we exchange phone numbers, because that's when you need them.
I have dealt with some real weirdos on CL and I am really glad they don't have my phone number.
I also almost never get scam emails anymore. I had assumed CL was filtering them or something. Maybe because you're NOT using their redirect you're getting more scams?