Functions as phosphatidylcholine:diacylglycerol cholinephosphotransferase that catalyzes the transfer of the phosphocholine headgroup from phosphatidylcholine (PC) to diacylglycerol, a major reaction for the transfer of 18:1 into phosphatidylcholine for desaturation and also for the reverse transfer of 18:2 and 18:3 into the triacylglycerols synthesis pathway. Belongs to the phosphatidylcholine:diacylglycerol cholinephosphotransferase family.