If you are running dbvisualizer on the ambari managed node, you need to add /etc/hbase/conf to the classpath of the connection. If you are running it from not managed node, copy /etc/hbase/conf to some local directory and add it to the classpath.
Please be more specific about the changes you have done. The error states that you did something in the command line and that's not that you need to do. Those changes should be done in the properties for phoenix driver. The place where you specify phoenix-client.jar you also should look for additional properties like 'extra classpath' and that's the place where you should provide the path to /etc/hbase/conf