If you've come across p129-fmfmobile.icloud.com and are wondering whether it's safe, the short answer is yes — but with an asterisk. This is a subdomain of icloud.com, which means it belongs to Apple. The certificate, hosting, and security headers all match what you'd expect from an Apple service. There's no history of malware or blacklisting, and the connection is encrypted properly.
So why the asterisk? Because this URL currently leads nowhere. The server returns a 404 error, meaning the resource you're looking for doesn't exist at this address. That's not unusual for internal or temporary Apple endpoints, but it does mean there's nothing to actually use. If you were expecting a login page, a file, or a service, this isn't it.
What does this mean for you? If you see this link in an email or message, it's not a scam in the traditional sense — but it's also not a working site. Apple doesn't have a public-facing service at this location. The safest takeaway is that there's no reason to trust this URL with any personal information, simply because there's nothing here to interact with. If you need an Apple service, go directly to icloud.com or apple.com rather than typing in subdomains you don't recognize.