I think I [male 37] caught my GF [ 35]

My GF and I live together and have been in a relationship for a long time. The other day she was feeling tired and decided to take a nap upstairs in the bedroom. I left her to it and got on with a few chores etc. After a couple hours I decided to go up and check on her. I went upstairs (from the top of our stairs you can see right into the bedroom but from the bed you can’t see if someone is coming) and as I got there I noticed she quickly put her phone down to her side and then ( in my mind) pretended to be asleep… once I was in the room she ‘woke up’… I mentioned straight away and confronted her that I saw her put her phone down just as I was walking in but she denied any wrong doing … we spoke about it for a while but she insisted it was all just coincidental timing and that there was nothing to worry about … but I am not 100% sure it was … am I being paranoid?