pithecophobia

— Nevertheless I beg your indulgence for describing a new kind of phobia which is now widely prevalent among the American public. It may be named pithecophobia, or the dread of apes—especially the dread of apes as relatives or ancestors. During the past few years this phobia has become almost pandemic; perhaps we have not yet passed the peak of its incidence, especially in rural communities.

— This is heightened in Brobdingnag because the monkey abducts Gulliver to a roof, which adds acrophobia (fear of heights) to pithecophobia, doubling the risky, frightening nature of this encounter.