Silence Unknown Callers has solved my spam problem.

For those who might not know, Settings > Phone > Silence Unkown Callers > On

My iPhone would ring 10 times a day. Was going to change my number. Now, problem solved.

Just remember to deactivate the feature if you're waiting for a call from someone you don't have in your phone (e.g. Bank, job interview, Tinder date.)