Catalyzes the key rate-limiting step in the CDP-choline pathway for phosphatidylcholine biosynthesis. CTP + H(+) + phosphocholine = CDP-choline + diphosphate Phospholipid metabolism; phosphatidylcholine biosynthesis; phosphatidylcholine from phosphocholine: step 1/2. Homodimer. Belongs to the cytidylyltransferase family.