The detection of calcification clusters in mammograms is of great importance for early diagnosis of breast cancer. For this reason, a large number of breast phantoms have been developed possibiliting the insertion of calcifications in simulated background images, which needs to be as realistic as possible to ensure the accuracy of results and a greater range of applications. In this study, we simulated three different densities of the breast parenchyma using paraffin gel, acrylic plates and PVC films and inserted hydroxyapatite grains above to simulate six calcification clusters. From the images acquired with a GE Senographe DR equipment, we selected an equal number of regions of interest (ROIs) with and without a calcification cluster added, totalizing a quantity of 136 ROIs. For comparison, and to validate the phantom simulation, the same number of ROIs was selected from the University of South Florida’s Digital Database for Screening Mammography (DDSM). Two observer experiments were performed by seven experienced readers using a high-resolution quality monitor where the observers had to try to identify which was a phantom or real image and if it had or not a calcification cluster inserted. Results shown that the hydroxyapatite calcifications are well hidden in the breast parenchyma simulated which has meant that the observers had more difficulty to identify the presence of the clusters for phantom images. However, there is the need to adapt the simulation of the image background so that it becomes more realistic.