Ahh, you’re now asking different questions and telling us a bit more - like you have got them set up as a stereo pair. But just to be sure: are they both set in one Sonos room as a stereo pair, or two rooms which you’ve grouped?
The Line Out you’re (correctly) using is the amplified output; the Phono connections are non-amplified.
If you’re only getting sound on one Era, make sure the cables are connected correctly. Pull them out and plug them in again. If still no joy plug the red connector into the right socket of line out, and the white into the left. If sound now comes out of only your other Era, there’s a problem with (a) the turntable, (b) the stylus connections, (c) the cable, or (d) the Sonos adaptor.