"Call/Cancel" popup in Google App
It seems more likely that this call button was actually just a part of the website. If so the fake button probably was an off-white color rather than pure white.
If your phone isn't jailbroken I wouldn't worry about it. Clear your browser cookies to be on the safe side but it's probably fine.
If you see any suspicious ads on your home screen or profiles being asked for you to trust then you should worry. If so reset your phone to factory settings  or to an iCloud backup.
I recommend using Safari for these activities and blocking popups. Make sure to use a VPN.