Sons father wanted his social security number, but claims he is not trying to claim him on tax return.?

There's a form that you have to give him in order for him to claim your son because you have custody and he doesn't. As long as it was a phone conversation and you didn't give him any tax forms you should be fine. And if his taxes do get accepted with him claiming his son when the IRS catches him he would owe backtaxes and that comes with a lot of fees and penalties.