We know Grasso physically had the phone. Tom told him to message Cliff to meet at Bailey's.
Reading reddit they are torn between Lizzie and Grasso, they think the leak may be Lizzie and she swapped the phones

They said that when she was going on about soccer patches and nicknames or w/e that she may be covering for motorcycle club patches. Motorcycle clubs have patches with nicknames.
There was also the comment Grasso made about staties being passed through, meaning they dont really do a deep dive when they are assigned to a task team.
Then there is Grasso, the main thing going against him is Perry has Ray's phone with the Flyers logo. How does Grasso not know that isn't Ray's phone? He should be able to tell. There's also the scene in the park where Tom tells Grasso to message Cliff. He is texting "ATT Mobility Service", which doesnt make sense. This is when he texts "Is that you?" before they pull over the couple looking for their dog. Could be a production error though
Either way, it had to be someone on the task team to swap out the phones. The boss chick from Goonies could be a red herring or working with the mole, but she couldnt have swapped the phones. Least I dont think she couldve.