Novel forms of nonvolatile memory, such as phase-change memory (PCM), promise low latency and small granularity of read and write access at high storage density. They also feature very high endurance. These characteristics make them highly desirable for emerging high-capacity (hybrid) memory applications such as in-memory databases and in-memory processing. In this work, we present the architecture, implementation and experimental performance results of an FPGA-based PCM memory controller for OpenPOWER servers. The memory controller leverages the Coherent Accelerator Processor Interface (CAPI) of the POWER processor in order to offer low-latency access to the CPU memory space. In addition, the memory controller implements an efficient management protocol that supports a dynamic size of pending read and write requests in order to offer high bandwidth under mixed-type workloads. We describe the architecture and implementation details of the memory controller and we demonstrate its performance using a prototype platform based on different types of OpenPOWER servers equipped with CAPI-enabled FPGA cards. The developed PCM controller is evaluated in terms of sustained data rates (MBps) and access latency (us). Experimental results are based on legacy commercial 90nm PCM chips as well as on accurate HW emulation of next generation PCM chips.