It was business as usual at the supermarket which gave Phoebe a hint that Shark and his team were not there yet which was not a surprise because she lived close to it compared to where Shark was coming from.
For a while, Phoebe hung around outside, waiting impatiently but her patience run thin and eventually, she decided not to wait. Rather than wait, she figured there would be no harm heading inside to do her own investigations. Even though Reid had said his death was an accident, the police would have questions.
They would have to ensure that he was not pushed deliberately or poisoned or even tricked into climbing to the top of the refrigerators. The supermarket itself would probably be closed for a while because a dead body had been in there for so long, who knew what other health risks were hiding inside.