Apparatuses, methods, and systems are disclosed for determining resources for phase tracking reference signals. One method (500) includes determining (502) a first set of resources. The first set of resources are used for non-zero power phase tracking reference signals for a first downlink transmission and zero power phase tracking reference signals for a second downlink transmission. The method (500) includes determining (504) a second set of resources. The second set of resources are used for zero power phase tracking reference signals for the first downlink transmission and non-zero power phase tracking reference signals for the second downlink transmission. The method (500) includes transmitting (506) the first downlink transmission using the first set of resources and the second set of resources. The first downlink transmission is transmitted concurrently with the second downlink transmission.