Monitoring fetal cardiac activity is a widespread method for assessing fetal well-being. With the rise of smart devices and after the COVID-19 pandemic the at-home monitoring became increasingly popular. However, evaluation and development of fetal heart monitoring systems are hindered by the lack of inexpensive, reproducible, and non-human test platforms. In this work, we present the design and validation of a low-cost abdominal phantom intended to mimic the acoustic and infrasonic properties of a pregnant abdomen, with a focus on fetal phonocardiography. The phantom was constructed from multi-layer silicone rubber–oil mixtures with differing stiffness to represent soft tissue and skin, and incorporated an internal low-frequency speaker as a controllable sound source. Its dynamic behavior was characterized using an optical laser-based vibration measurement, piezoelectric, and multiple microphone types over the 5–100 Hz frequency range which are relevant to fetal heart sounds. A linearized fundamental-frequency analysis was employed to estimate frequency responses and isolate the transfer function of the phantom. Results show pronounced high-frequency attenuation and a resonance around 22 Hz. These findings indicate that the proposed phantom provides a promising baseline for validating fetal heart monitoring instruments, although further refinement and characterization are required to fully understand its behavior and to enable realistic reproduction of fetal heart signals.