Cloud providers perform flow monitoring to get insights from the network traffic flows, often using coarse-grained packet counters or packet probing. These approaches give partial information from ongoing flows or introduce significant overhead if the probe packets cross multiple hops with diverse delay and bandwidth to reach the traffic collector. Recently, In-band Network Telemetry (INT) offered by programmable networks, e.g., P4, has gained attention by providing fine-grained network telemetry. Current attempts on INT are inflexible in collecting telemetry for customs flows according to the desired interval. This letter proposes P4FLOW, a flow monitoring tool for cloud provider networks implemented on programmable data planes. P4FLOW allows the providers to monitor a set of desired flows according to their needs. It reduces at least 1.6× the overhead of telemetry packets compared with the existing approaches.