Many people are getting error saying: “Safari can’t open the page because it can’t find the server” although they have full signal. This is a common problem, caused by the way iOS handles the Domain Name System (DNS). DNS converts URL to the correct IP address and when you’re iOS is not handling the requests correctly you will face this problem.
To test if this is your problem, enter this into the address bar: 18.104.22.168 It should load Google. By directly entering the IP address, you eliminate the need for the DNS.
Here is how you fix this:
1) go to Settings> Wifi
2) Tap the blue arrow to the right of the network’s signal strength meter
3) Replace everything in the DNS field with 22.214.171.124 or 126.96.36.199 ( Google’s Public DNS)
If this problem persists you may want to try to reset all networks settings by going to Settings>General>Reset>Reset network settings.