Question: how to fix poor wifi connection on iphone 6?
Answer:  Perform a Forced Restart: Hold down the Home and Wake/Sleep buttons at the same time for about 15-20 seconds until the Apple logo appears. ... 
 Reset Network Settings: Settings > General > Reset > Reset Network Settings. ... 
 Reboot Router/Modem: Unplug from power for 2 minutes and plug again.