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Yeah, like Miriam, I feel like I'm not understanding some key aspects of this situation. Why is the old site still live. How different is the new site? How is the old site being used? My bigger concern, from a traditional SEO standpoint, would be that the old site might have pages/assets/etc. that are duplicates and could harm content on the new site. It's hard for me to see how the new site could be completely different and still be the same core business, honestly. In terms of the phone number, though, I don't think Google really associates that with any kind of spam or malware signal. The fact that the phone number is on another site probably isn't going to harm your new site, in a core SEO sense. If the owners of the old domain started to generally make trouble and try to ruin your reputation, then having people connect the number to you wouldn't be great. Again, I'm not clear on how bad the situation is. It's remotely possible Google could use the phone number to connect the sites, in the sense of seeing them as owned by the same people, but I think that's far-fetched. That would probably only come into play with something like a link network. So, short answer is that I think the risk is small, but I hesitate to say that decisively without knowing more.