Phase coherent transport phenomena are studied in a magnetic, two-dimensional hole system confined in a strained InAs quantum-well structure. At low magnetic fields we observe a well pronounced weak antilocalization signature, demonstrating that magnetic ions in proximity to the itinerant holes preserve phase coherent transport, although magnetic effects like the anomalous and planar Hall effects are present at low temperatures. From fits to the conductivity correction, spin and phase relaxation times are extracted in a large temperature range from 200 mK to 16 K. From the dependency of the spin relaxation time on temperature and in-plane magnetic fields, we conclude that the Dyakonov-Perel mechanism is the dominant spin relaxation mechanism. The metamorphic growth of the heterostructure causes a nonplanar quantum well that enables the formation of magnetic barriers in the presence of a parallel applied magnetic field. Transport through these magnetic barriers causes a positive magnetoresistance superimposed on the weak antilocalization signal.