What is your connection method?

The Arc uses HDMI ARC, not standard HDMI, that might possibly be one issue. 

Make sure the audio cables from the turntable are connected to AUDIO IN on the Port. Also be sure the switch on the back of the turntable is set to LINE not Phono. In the Sonos app under the Port’s Line-In settings, set the Autoplay Room to the room associated with the Arc.

Hmmm. I may have misread that, sorry. Your turntable is connected to the Sonos Port, correct? Is this turntable going through a pre-amp, or does it have a switch that you’ve set to ‘Line’?

Did you choose Line in as a source on the Arc? Sonos views the Line in as a source to the system, not to the Port only.

I switched it to line. On the app it shows line-in connected but still no sound out of the arc. I did auto play. Is there something I need to change in the app for the Arc?

WHERE did you turn on autoplay? In Arcs settings or in Ports settings?

You will have to turn it on in Ports settings and to select there Arcs room as destination for autoplay. Also you can set a preset start volume for autoplay. 
As a test you also can try to do it via grouping. Therefore set Ports room itself to autoplay destination and when ports playback view shows it is playing, set up Arcs room to Ports room as a group. 
If both fails, there might be a network issue e. g. one of the devices is connected to the network via a wifi repeater. 

I finally got it to work. I did all the things and couldn’t get it to work. Finally, I unplugged it with the correct settings and once it rebooted it starting playing. Thanks guys!!!