For her Lock Screen she has a picture of Nickit doing something cute, or her entire team (like a photoshoot) or maybe Victini eating a macaron or something adorable :3c

Her Home Screen is a little more personal, and it's probably a photo of herself with Rose and Oleana, I'm not sure if they have many photos all together but maybe they took one after one of Briar's first concerts, after sending her flowers backstage like people usually do for idols lol But she's too embarrassed to admit she has feelings so she would say her Home Screen is a picture of herself because she's a narcissist or something