I have an iPhone 5s that was bought several months ago. For some reason, it is quite slow on the wifi in my house - noticeably slower than 4g/LTE speed - and has been this way from the beginning. Other devices (Macbook, iPhone 4) do not have this problem when used from the same location. Also, the phone seems to work well on other wifi networks. Are there any ways to troubleshoot this?
You might want to follow Apple's steps in troubleshooting generate Wifi issues.
In addition, try resetting the iPhone's Network Settings by navigating to Settings > General > Reset > Reset Network Settings, then restart the iPhone and re-connect to the WiFi network.