My spouse has started keeping the phone on silent

My spouse has been coming home from work later than usual for the last two months, and their phone is always on silent. At first, they said work has been busy, then they mentioned their phone was in service, but I can't help but think they are just making excuses. If I ask, they have an answer ready; if I don't, it just grows inside me. Is it unfair to feel suspicious? Or should I trust my instincts?