How to remove JanusGraph index?

but the index status is installed,how to change the status to registed and then disable it to remove it please help me ,

  GraphTraversalSource g = janusGraph.traversal();
    JanusGraphManagement janusGraphManagement = janusGraph.openManagement();
    JanusGraphIndex phoneIndex = 
    janusGraphManagement.getGraphIndex("phoneIndex");
    PropertyKey phone = janusGraphManagement.getPropertyKey("phone");
    SchemaStatus indexStatus = phoneIndex.getIndexStatus(phone);
    String name = phoneIndex.name();
    System.out.println(name);
    if (indexStatus == INSTALLED) {
       janusGraphManagement.commit();
       janusGraph.tx().commit();