A Sonos Port is designed to get things in to the Sonos ecosystem.
A Sonos Amp is designed to do much the same, with the added power to drive external speakers, which is why it is more expensive.
All you need to connect a Turntable is a Sonos line in. Both the Port, and the Amp have one, as do several other speakers, some requiring adapter cables.
The Sonos line in, on all devices, is essentially the same, being based in software, so one device is not any better than another. The only significant difference is the form factor of the line in. Anyone who has said that one device is different is mistaken, unfortunately.
Sonos delays any line in, except TV video, by 75ms, so that the incoming sound can be synced across any number of speakers. When you group another ‘room’ with a TV input, you’ll find that delay, as the Sonos system has to shift to multiple room synchronization.
Since Sonos is expecting a line level line in, any turntable that outputs a ‘phono’ level will need a pre-amp, to raise that output. Many turntables theses days include a pre-amp built in, and include a switch so that you can change the output from ‘phono’ level to ‘line level’ output.
All of this is covered in the FAQ, as well as this area of the forum.