With antibiotic resistance on the rise and expected to be a major health problem in the coming years [1], we are looking for alternative ways to treat bacterial infectious diseases. This work is in the scope of phage therapy, i.e. the use of therapeutic highly specific bacterial viruses called bacteriophages. As with the antibiotic susceptibility test (antibiogram), a phage susceptibility test (phagogram) that allows rapid and reliable testing of phage collections to identify the optimal phage(s) to administer to patients is highly desirable. Accordingly, we show here preliminary results of a new method to perform a phagogram with phages trapped on an optical chip. The system used is a silicon-on-insulator photonic chip containing L3 slotted 2D hollow photonic crystal cavities topped by a micro fluidic system allowing the transport of phages in their vicinity. The light confined in the cavity allows the trapping of nearby objects by gradient forces while the light collected at the output of the chip allows to deduce information about the trapped object. Circular 2D hollow cavities have been used previously to trap bacteria by means of a self-induced back action (SIBA)[2] mechanism and have demonstrated classification, and viability assessment of bacteria[3-5]. By changing the cavities to a linear cavity (SEM Image on figure 1: A) with an optical field (simulated near field intensity of the resonant mode on figure 1: B) more suitable to the trapping of 100 nm size viruses, we obtain photonic cavities allowing to trap phages and to distinguish different phages according to their families.