Integrate phono with 24-bit/48kHz?

First, why would you want to do that? You are taking a low dynamic range and limited frequency analog signal and encoding it in a digital format that will result mostly in wasted file size with no impact on sound quality. 

CD quality lossless encoding is still far more capabile of storing/streaming audio than the vinyl is of playing it so there is no audible reason to use higher rates and depths. 

You could probably use an external (not Sonos) analog to digital encoder set to a nigher bitrate and depth and feed that into the Sonos system with something like Plex.

In non-audio terms, you are planning on feeding a 1/2 inch garden hose into a 3 inch firehose but thinking you need a 6 inch hose as the 3 inch one won't carry all the water the 1/2 inch hose can provide.