Recording phone calls made to and from your phone is a good idea in this day. It can be particularly useful when you have a disagreement with someone regarding the clarity of a conversation. You can also use a recorded phone call to pursue a legal case.
There are dozens of mobile applications for Android and iOS that allow you to record calls on your mobile phone. Many of them allow you to choose between recording all calls by default or only recording calls from certain contacts.
Visit Google Play Store and explore the various phone call recording applications.