Voice Recorder isn't for recording phone conversations. That is more for just recording things for yourself, or conversations right where you are (say you and a group of people in a room).
You need to search for call recording apps. Personally I don't use them. Most states have laws about recording conversations without the other person knowing they are being recorded. In some it is quite illegal, so be careful and check what the laws are in yours, as well as the laws in whatever state you are recording a call to/from. This, of course, is if you are in the USA. If not, well then I would still suggest you check the laws where you are.
A quick search on Google Play brought a huge list of apps saying they can record calls. A few even saying they will do it automatically, like "Automatic Call Recorder by recorder & smart apps" and "Automatic Call Recorder by Appliqato". I just typed in... Free Call Recording
Now, granted most of them may not be free, or will contain ads, so it is up to you if you wish to put up with that. Or you can try paid ones that may not have ads.
Another route is to take/make calls through say google voice, which allows for recording your calls.