Wife possibly cheating

My wife (27F) and I (25M) have had a rough time on our marriage for the past year. We recently had a conversation about cheating. During the conversation it seemed like she was justifying why either one of us would cheat, after that she quickly said that she hadn’t cheated. Since I’ve been home I’ve noticed some small habits she has that changed from before I left. She puts her phone face down, which she never used to do, she keeps it with her at all times, and when she’s asleep she puts it under her pillow, or somewhere where she would wake up if I tried to take it. She’s told me that I couldn’t use her phone when mine was dead, and told me that I make her feel like a shitty wife if I ask to look through her phone.

Tl;dr I feel like my wife might be cheating on me.

Update: We talked last night, she offered her phone after I voiced my concerns. There was no evidence of anything out of the ordinary, no evidence of cheating. She said she puts her phone under her pillow so she can feel the vibration when her alarm is ringing, her phone has a big camera, she doesn’t have a cover for them and that’s why she puts it face down.