Old phone ? Over thinking this ?

So I bought my boyfriend a new phone for his birthday. (Week ago) His old phone still has service to the the 18th but I haven’t seen him using it. He’s been keeping it in the car door. He works monday to Friday and I’m a stay at home mom with our kids. Last night I told him I was going to my moms for dinner with my family and when I got there I realized the phone was gone out of the door. (He ended up coming with us, he thought he might not at first). Fast forward to when we got home I noticed it was on the floor by his side of the bed, somewhere I never really go. I didn’t think much of it but then I went to go shower and he came in the bathroom and told me he was going out to smoke, he smokes in our car. So I was curious about the phone, I looked and it was gone. So he took it back to the car. Am I over thinking this or is it suspicious ?