There may not be a fix. Is your phone capable of 5ghz wi-fi, is your router capable of 5ghz wi-fi? If one or neither of them are there's no way to make it faster or more stable. 2.4ghz is actually the same signal it's just not capable of sending or receiving as much data as a 5ghz frequency.
The easiest way I've found to explain radio frequency is to picture the frequency as a board.
The number associated with a radio frequency is basically the size of it and it's size determines how much data it can carry as well as how obstacles effect it's signal strength and how much data it looses over distance and because of running in to, going through, or around obstacles (obstacles are anything in it's path: Walls, boards, doors, metal is a big obstacle because metal is very dense as well as reflective so a radio frequency bounces off of metals instead of penetrating or going around them).
Picture a 2.4 frequency being a board 2 feet long by 4 inches wide.
Picture a 5ghz frequency being a board 5 feet long by 5 inches wide (significantly bigger).
A 2.4 frequency (board) carried across a persons shoulders long ways is going to easier to carry and maneuver through doorways and windows with than a 5 foot long board 5 inches wide. This is why a smaller frequency is sometimes better to use because it's not effected as much as a bigger frequency is by obstacles.
It's also why wired connections are more stable. Wired connections are not necessarily faster they're more stable and reliable because they have a straight, concealed, protected, and controlled path to travel. Wireless connections have everything you see to maneuver around, penetrate, bounce off of, and get past.
If there is a lot of structure between you and the router on your phone and your computer is either wired or doesn't have as much in the way that's why and the only thing you can try to do about it is place the router somewhere that would be a closer and less obstructed path to where you normally are with the phone.
Radio frequencies are also very similar to how water reacts to something being dropped in to a body of water, how an object has the center point where it hits and enters the water and ripples of waves fan out from that point of impact.
In a radio wave the point of impact of the water is the antenna on the transmitter sending the signal (the router for wi-fi) and radio signal frequency is the same exact shape and form as the ripples and waves in the water except they're invisible because radio waves are in the air.
Just like water hits an obstruction like a rock the wave gets effected by that object a radio wave gets effected the same way by objects in the environment.