Bf won’t show me his phone

So I’ve been with my bf for two and a half years and this whole time he’s always been super protective over his phone, he’ll always turn it away from me when he’s unlocking it or when he gets a notification, he’d rather leave than to show me his phone. I tell him he’s clearly hiding something and he denies it, but why else would he be like this over his phone?

I got fed up tonight bc we’ve been going through a rough patch and I have a gut feeling he’s cheating. He’s still refusing to show me his phone, Idk what to do or think at this point.