A Google Play search for "cell phone spam blockers" brought up a number of apps of which I chose Truecaller due its good reviews and high number of downloads. It has only been on my phone for about a week and already has warned me of several spam calls which I have blocked for future calls.
The software has a number of other features which I am beginning to explore but it is the spam blocker that I use the most. It's still early but as of this writing, it works as advertised. If you have tried similar apps and like them, please feel free to comment in the section below.