(You Can) Call on Me is a side mission in the video game, "South Park: The Fractured But Whole".
Plot details follow.
Help Call Girl fix her phone.
Call Girl will contact you and ask to meet you at the bathrooms by The Playground. Talk with her there.
Then, follow her to D-Mobile. Head inside to find that Crab People have taken the workers hostage and overrun the store. Then, you will need to fight these enemies. Start by taking out the first two crab people. There is nothing notable about their attacks. Take them out one at a time to manage them effectively. Then, after they are down, Manager King Crab will appear, bringing new crab people with him.
Focus all your attacks on Manager King Crab. Take him out and the fight is over. Achieve victory to receive the Subdermal Mutation DNA and the Call Girl Character Sheet. You will also be able to take a selfie with each employee afterwards.