Your problem is not the phone.
Rather, your problem is the WiFi router.
You need to get one that supports at least 1900mhz frequency on the AC spec.
https://www.amazon.com/TP-Link-Wireless-Dual-Band-Archer-C9/dp/B00PDLRHFW/ref=sr_1_1?ie=UTF8&qid=1525409571&sr=8-1&keywords=tplink+ac1900
The AC standard will let you run as fast as your Fiber connection is, with perhaps a 10-20% speed degradation due to environment.
Also, the speed metrics may be a bit deceiving.
Speed on the Internet service is measured in Mb/s.
Download speed on a Browser is measured in MB/s (note b vs B).
There are 8 bits (b) in a Byte (B).
So you will have to calculate speed by dividing 250 million bits by 8 and possibly deducting another 10-25% (environment) to get the speed you theoretically should be getting.
So theoretically, you should be getting 27-31MegaBytes per second download speed.