Telefonica Spain APN Settings for Apple iPhone 6s Plus

In the main menu, tap Settings
Tap Cellular.

Check that Cellular Data is turned on.
Tap Cellular Data Options and then Cellular Data Network. 
(If this setting does not appear on the device, it has not unlocked and settings cannot be configured manually.)

Go to Cellular Data section and enter below information

APN: movistar.es
Username:
Password: MOVISTAR

Go to LTE Setup (Optional) section and enter below information

APN: (Leave Blank)
Username: (Leave Blank)
Password: (Leave Blank)

Press the Home button to save the APN and exit to the main screen.
Restart the device.