The numbers show consumer demand for handsets in China remains low, and that companies such as Huawei Technologies Co Ltd, Xiaomi Corp and Apple Inc will have a tougher time than before convincing customers to buy their latest products.
Phone makers shipped 24.4 million handsets in July, down from 33 million a year earlier, according to the China Academy of Information and Communications Technology (CAICT), a state-backed think tank.
That continues a decline through the summer as May, June, and July shipments fell by 10%, 16% and 35%, respectively.
China is one of the few countries where retail outlets have re-opened almost fully after virus-related lockdowns, making it a key market for hardware brands this year.
Both Huawei and Apple are expected to announce new flagship devices this autumn.
Apple and its rival smartphone brands do not publicly release regional shipment data.