Please be gentle with me! 🙏

Yes.  It’ll sound better both as a streamer and as a DAC so he’ll get improvements on both counts.  He should also be using a quality streaming service like Qobuz or Tidal.  

It will not only sound better, but also be a lot more convenient. 

Yes. It also sets him up into the contemporary world of streaming. Qobuz is the best sounding service with the most high resolution recordings.

In addition this could be the example you need to start mapping out your future audio. While investment must be at least equal into the streaming world (streamer + DAC) to equal the sound quality of vinyl (tt + phonostage). You are freed from severe constraints of vinyl: a tiny library of disks, surface noise, and getting up all the time. It is good to get into this world as soon as possible. Looking back on the fifty years I spent listening to the same few disks (4,000) seems quaint in retrospect.

So I will disagree here.  It depends.  The DAC in the Node may or may not be better than the DAC included in the amp.  And the phone may or may not be better as a digital transport into the DAC.  I was using an LG phone in exactly the same way your son is.  I replaced it with a Node because I didn’t want my phone tethered to my system.  There was no obvious sonic improvement 

Oops.  I misread and thought he was using the DAC in the phone.  Not sure if DAC in the Node would be an improvement or not.  My bad.