Why is my Wi-Fi signal so weak?

My Wi-Fi router is located in the basement, and everyone upstairs (kitchen living room etc) gets a pretty good for the most part Wi-Fi signal on their phone or laptop/ ipad. I have a bedroom located in the basement, the router as i said was located in the basement and is the opposite end of where my room is. About 15-20 feet away. The problem is that on my iPhone i get little to no signal ( i have a 5S) however its not just this iPhone, it did it with my iPhone 4S as well as my galaxy phone. I have a laptop as well, but it will get perfect Wi-Fi signal while my mobile devices get nothing. If i move my iPhone a little closer to in the direction of the router it sometimes boosts the signal, the weird part is that i only move it like an inch and it gets signal then it goes back down again. There has to be a reason why my computer gets perfect signal and my mobile devices get little or no Wi-Fi when i'm only 15 feet away. And i know i'm less than 25 feet away because my Bluetooth stereo in my room has a 25 foot range and still plays when i'm standing the by the router. This is becoming really annoying as i have to use cellular data even when i'm at home the extra data that i'm charging is really starting to add up. Is there any solution to this problem?

Get closer to it

The iPhone (and any other mobile device) has a much smaller antenna, and thus a smaller range, than a laptop has. Is it possible for you to move the router onto the first floor? The flooring or other radio devices can cause some interference where the one inch can actually make a difference because of the frequencies interfering.

Get a new one durr

You should check your router signal in router setting on your router from your computer. I personally have a belkin router and i can control the bandwidth. If you can put the router in your room, a lot of things will mess with Wi-Fi signals as well.