I was driving to work and stopped by my local gas station to fill up. A dude with a family/children organization shirt came up to me (probably mid 20s to early 30s) and asked for some money. I gave him $10 but then he asked for my phone number.
He didn't give a reason, nor did I ask (which I should have), but I gave him my real phone number. He had no contact with my personal phone, but he put my number as a contact with my first name (no last name).
He then walked off, but I drove near him and he was immediately on the phone behind the gas station. I'm afraid of bank scams, medical fraud, etc. So I ask all of you: what can he do with my phone number and first name? Should I change my phone number across important applications and social media? Please help.