Significance A consortium of sequenced human gut bacteria was introduced into germ-free mice followed by a “staged” phage attack with virus-like particles purified from the fecal microbiota of five healthy adult humans. Unique phages were identified attacking microbiota members in nonsimultaneous fashion. Some host bacterial species acquired resistance to phage attack through ecological or epigenetic mechanisms. Changes in community structure observed after attack were transient. Spontaneous induction of prophages present in seven bacterial taxa was modest, occurring independently of the phage attack. Together, these results reveal a largely temperate phage–bacterial host dynamic and illustrate how gnotobiotic mouse models can help characterize ecological relationships in the gut by taking into account its most abundant but least understood component, viruses.