Catalyzes the conversion of 5-alpha-acetoxy-10beta-ol to 5-alpha-acetoxy-10beta,14beta-dihydroxy taxadiene. Also acts on taxa-4(20),11-dien-5-alpha-yl acetate. 10beta-hydroxytaxa-4(20),11-dien-5alpha-yl acetate + H(+) + NADPH + O2 = 10beta,14beta-dihydroxytaxa-4(20),11-dien-5alpha-yl acetate + H2O + NADP(+) Optimum pH is 7.5. Alkaloid biosynthesis; taxol biosynthesis. Belongs to the cytochrome P450 family.