If this turntable has a switch for a pre-amp, make sure that switch (sometimes under the platter, or on the back panel) is turned to line, and not phone. If it doesn’t have a built in preamp, they’re relatively inexpensive, but you’ll need on to boost the signal to a level that Sonos can work with. Then connect the two RCA jacks to a RCA to 3.5mm cable (stereo), and plug that in to the back of your PLAY:5 gen 2. Follow the instructions in this FAQ.
I’m not sure why customer service would say that, but a non-Bluetooth capable Sonos speaker will always need a cable connection to the Line-In to play external sources like a turntable.
My speakers are not near the turntable. My old turntable connected to the system wirelessly through the Connect component, which I no longer have, and Sonos no longer carries.
The Sonos CONNECT was replaced by the Sonos Port.
Note that the new Era 100 can be used as a less expensive Line-In source than the Port. You would need to purchase the Sonos Line-In accessory as well as the Era 100.