Five years after Voice of the Faithful took root in the basement of a Boston-area church, the group’s place in Catholic history remains unclear. Group leaders count 120 affiliates and 35,000 members. The lay-led grassroots group says it has achieved significant feats — tougher sex-abuse laws, increased transparency in some dioceses and more lay involvement in parish governance. But the group also promised to promote “structural change” in the Catholic church — an institution that takes pride in standing firm on shifting cultural sands. Some Voice of the Faithful members, frustrated with the pace of reform, want to confront the Catholic hierarchy with broader demands and sharper criticism. Others counsel patience and cooperation, said group president Mary Pat Fox.