The Proton Pack, designed by Dr. Egon Spengler, is a man-portable particle accelerator system that is used to create a charged particle beam - composed of protons - that is fired by the proton gun or the "neutrona wand". It is a positron collider, it presumably functions by colliding high-energy positrons to generate its proton beam. The beam allows a ghostbuster to contain and hold "negatively charged ectoplasmic entities". This containment ability allows the wielder to position a ghost above a trap for capture.
The minimalist icons look tiny on my dock compared to yours. I'm also guessing you made your own icon, because there is no dialer phone icon.