If a guy adds you on Facebook but doesn't give you his phone number, and when you try to voice call him on Facebook he doesn't respond is that a red

Lots and Lots of scammers out there trying to steal your information. They friend you and as soon as you accept, they note all your friends, and download all of your pictures. They can then impersonate you and send friend requests to all your friends and continue collecting identities.
Be careful who you friend.