A phosphorus-oxygen lyase found primarily in bacteria. The enzyme catalyses the cleavage of a phosphoester linkage in 1-phosphatidyl-1D-myo-inositol to form 1D-myo-inositol 1,2-cyclic phosphate and diacylglycerol. The enzyme was formerly classified as a phosphoric diester hydrolase (EC 3.1.4.10) and is often referred to as a type C phospholipases. However it is now known that a cyclic phosphate is the final product of this enzyme and that water does not enter into the reaction.