What’s connected by Ethernet? Sonos or your phone? 

Sonos hasn’t blocked anything. The system works perfectly fine on Ethernet, in “wired” (SonosNet) mode. 

Sonos can no longer directly play files stored on iDevices, owing to changes made to iOS some time back.

If your phone is on WiFi and it can’t see Sonos when wired then it’s likely to be a router/AP problem. Kindly describe your network arrangements.

Why would my phone be connected to ethernet?

my sonos is directly connected to my network switch. It always has been. I’m able connect to it with my apple tv. The sonos app on iphone simply does not see the SL One.

Have you tried unplugging the One SL from power for a couple of minutes and rebooting your router and phone?

If you want to play music stored on your phone to the One SL, you need to play the music over AirPlay.

I asked because (a) there are Ethernet adapters available for phones and (b) there was some ambiguity in your OP.

If this is a new phenomenon follow the instructions above. If it’s never been able to see the speaker then you have network issues preventing it. The most common are a badly designed router which blocks multicast traffic between segments, or a deliberate (or accidental) division of the local network into multiple subnets.

Where is the WiFi coming from? Do you have a mesh WiFi? 

The app on the phone can only communicate with what it can “see” on the network. You need your phone (and, thus, your Wi-Fi) to be in the same broadcast domain as the Ethernet part of your network.

There’s little benefit to splitting them apart, performance wise, because your Wi-Fi access point will only bridge traffic that needs to cross between the wireless and wired sides (ie broadcast, and anything between specific devices on the two sides).

If you think it is all one network, then check that your Wi-Fi doesn’t have any “station isolation” features enabled, as they would prevent wireless devices communicating with anything else on the local network too.