Read Mail keeps marking as unread
So I’ve been having this problem for a while now. My mail, on my iPhone ONLY, keeps saying that I have unread mail. I constantly check my email and I’m always getting rid of unnecessary emails and sort out my mail(as I am a student) and once I leave the app, it shows that I have unread mail. It’s not my network because I connect to WiFi and it still is the same problem. Yet, if I use my MacBook, I can easily mark my mail as read with no problems. I would like to mark my mail read on my phone as I find myself waiting for important emails on the go and don’t want to take my laptop with me EVERYWHERE I GO. Does anyone know how to change this?