Op there is always a debate on whether to confront.
If you ask for the phone, please think ahead to how you are going to handle this. He will refuse, and make every excuse not to give it to you, unless he has already taken the precaution of deleting things. If he refuses, are you really and definitely going to chuck him out? Because if you change your mind in the ensuing melee, you wont find out for years, maybe, and your suspicions wont go away.
I ask you to consider this carefully, because so many women think that is what they will do, and in the event and the debate and discussion, and the denial, and the possible gaslighting that you dont even see yet, they are persuaded against it, or think better of it.
If he hands it over and you find nothing, I still believe that you wont give this suspicion up, regardless of his future behaviour. That is because your intuition is everything, especially that first intuition, before you have spent any amount of time reasoning and rationalising with yourself.
If you want to be absolutely certain that he is having an affair, if that matters to you, you have to be more circumspect. You may need to have him watched or followed, or ask someone at his work (you probably dont know them yet, after a year).
I say this because it happened to me, and it was five and a half years before I got the truth. By that time, I was stressed, then depressed, and resentful, and miserable. I had managed to isolate myself somewhat, and bore my wonderful friends rigid, and had allowed my work to tail off to part time, as I believed that my stress and anxiety was related to having too much to do and a work obsessed h. And by the end, just before I forced a confession, he used the very fact that my work had tailed off because of all this shit, to suggest that I just imagined other women because "there was nothing else in my life".
Even now, if I put the length of my h's infidelity in a mn post, I have to add that half a year to the five. Because I am outraged and regretful about every single minute of it.