It was one of their later missions together, the first one where Phil was working with them in the field after Loki had stabbed him. There was a suspected HYDRA cell based in a night club in downtown New Jersey and Strike Team Delta had been sent to take care of it. Phil was playing the part of bartender, had been for a week now, he was the one that had the lowest risk of being recognised as SHIELD as he always worked in the shadows.
Clint and Natasha were patrons of the club, passing acquaintances that didn't know each other well enough to hang out together. Someone in the ranks of SHIELD obviously had a sense of humour as they had deemed this mission to be called 'Selfie' and all the codes they were supposed to use were selfie related. Clearly, SHIELD had started recruiting teenagers.
Natasha was currently complaining about Jason, a guy that she was conflicted about and unsure whether he was chatting to another female in order to make her jealous. This was code for, "I have him in my sights." As she went on to say that he had been totally texting her all night, last night it meant, "He's on the phone."
When Clint heard that Nat wanted to smoke a cigarette, he knew that it meant the mark was going outside. That was Clint's cue to pick up the trail as Natasha had to 'stop for a selfie'. Otherwise known as a picture of their mark. As Clint made his outside he started talking about the different 'filters' he should use. XX Pro being bullets, Valencia being tranq bullets. Asking whether he should take the selfie he had 'posted' down was getting confirmation from Phil that the mission was to proceed.
When Clint had taken the mark down successfully, Natasha got a text from 'Jason', they had taken a good 'Selfie'. The undercover part of the mission was over, Phil could stop making people drinks and listening to their problems, Clint could use his bow again and Tash could go back to her project of collecting various weapons to own and be proficient at.
A good selfie indeed.