Hello,
You would need to use the Strip Dial Character feature of Zoiper for iOS. This is required due to the fact that when you are saving numbers to your Contact list iOS is adding specific symbols - dashes, brackets, empty spaces, etc., according to the region settings.
To use the Strip Dial Character, go to your account configuration and open the Number rewriting section, then add the empty space and other symbols that you would need to strip, but are not present. Save the settings and you should be ready to make calls properly from the contacts.