Only use the SD cards specified by Phoenix, purchased directory from Phoenix or from a reputable vendor. Also see the FAQ “SD Card Specifications.”
In general terms, Phoenix receivers record data using SDXC SD cards, 64GB or larger, with the factory-format ExFAT. We have carefully selected which cards we support, and done extensive testing to ensure proper function and compatibility with the Phoenix hardware and firmware driver. Other cards may work (or may appear to work), but Phoenix recommends and supports the select cards we have specified.