You should take a look in the Igros Moshe, for example, to see the choice descriptions of Reform and Conservative by the great Rav Moshe.
Here are some other examples:
Agudas Harrabonim, March 24, 1997:
The Reform and Conservative are not Judaism at all. While their adherents are Jews, their religion is not Judaism. Despite their brazen usurpation of the titles ‘Judaism,’ ‘Jewish heritage,’ ‘Jewish tradition’ and’ Jewish continuity,’ Reform and Conservative are not Judaism at all. They are outside of Torah and outside of Judaism.
Dr. Harold Jacobs, president of the National Council of Young Israel, July 12, 1981:
“By rejecting the standards of Jewish law and tradition, it is the Reform and Conservative groups which have divided the Jewish people and caused needless human suffering through invalid conversion, marriage and divorce procedures which have thrown a shadow over the Jewish identity and marital status of thousands of innocent men and women. It is to avoid further damage and human suffering of this kind that we must reject Reform and Conservative demands for official religious recognition in Israel.”
Rav Yaakov Perlow, Novominsker Rebbe, Rosh Agudas Yisroel, May 27, 2014: