“My partner is secretive with his phone”

What could be going on

Compartmentalisation: He may keep parts of his life in separate boxes; check what else he keeps hidden.

Lies easily without discomfort: Check whether you've caught him lying in other areas.

Shame: He may hide something he's ashamed of, not necessarily an affair; check what changed and when.

Boundaries: Some privacy is normal; check whether it's new behaviour or how he's always been.

Confirmation bias: Once suspicious, everything can look like proof; check what you'd expect to see if innocent.

Mistrust/abuse schema: Fits if past betrayal makes you read secrecy as cheating.

Also said as

• he hides his phone and changed his password
• she takes her phone everywhere, even to the bathroom
• why is my boyfriend so protective of his phone
• I think he's hiding something
• my boyfriend hides his phone from me
• my husband keeps his phone face down