Wifi- doesn’t connect to iPhone 6 in certain parts of house but IPad does?

Hello,

I’ve been having trouble with wifi connections with my iPhone 6. You see, in certain parts of the house the wifi doesn’t connect (my room,study room). I thought maybe it was a problem with the wifi so I restarted the router. The wifi still wouldn’t connect on my iPhone in my room. I have another apple device, a iPad. The wifi connects just fine when I’m in my room with the iPad, even though it’s a super old model. I don’t understand why my iPhone doesn’t connect to the wifi? If I move rooms it’s works, just not in my room and the downstairs study room (living room and kitchen work fine). I’ve tried restarting network setting, all settings, doing a soft reset with the wifi off,forgetting the network. Nothing works. It’s been persisting for the past two days, and it happened last week too. Usually it works if I reset the router but it’s not working thing time. What do I do?