For example, when I'm in my bedroom, my macbook will have full Wi-Fi bars, my girlfriend's iPhone 6S plus will have full Wi-Fi bars, but mine will have only one, and eventually disconnects altogether after a couple minutes. I've tried taking the case off and re-booting the phone - doesn't help. I've also tried making my phone "forget" all Wi-Fi networks, then reconnecting. And yes, my phone is connected to the same network as the other devices. Thank you!
Added (1). Also - my GPS locater has a very hard time finding where I'm if I'm not connected to Wi-Fi. I have AT&T, and so does my mom. When we're standing next to each other, her iPhone 5 knows exactly where we're, while mine hardly knows what town we're in (giant blue range circle).