But "Zeiss optics" itself was also an empty marketing boast of Nokia and other colaborators. Not that different in performance from regular third party or even OEM optics, and the phone's sensor wouldn't be able to show any discernible difference anyway.
Isn't the iphone photo software lacking somehow? Maybe it was the software? I found a big difference with that phone. Very vivid photos. Not an expert but could it have been some "contrast" setting?
Or just higher saturation as a default.
Better lens optics can help with contrast or reduce fringing and such issues, but not to any extend that a Zeiss versus some regular current iPhone or Pixel or Samsung or Redmi lens would make any real difference to the picture.
Such processing side differences, on the other hand, can have a huge effect - and vivid colors is something directly affected by this.
A better sensor can too, but not very likely a sensor from 10 years or more ago is better than a current modern model. Though there are some changes some people prefer (CMOS vs CCD - though Nokia since the mid-00s had also switched to CMOS like the whole industry).