while you went to shower you did the big mistake of accidently leaving your phone unlocked on the table.

dabi and Shigaraki walk into the room and see your phone, and being them decided to look through it.

[Dabi] heh, look who left their phone out. [Shigaraki] I'm looking first Shigaraki grabs your phone. Dabi just rolls his eyes and looks over Shigaraki's shoulder.