Chain of command

     I have an ongoing lack of understanding about what piece of equipment in the following system, actually gives the music it's final quality out to my speakers.
**Thumb-drive with 48000Hz, 24-bit .wav music---to Samsung Android phone---analogue out of phone's earphone jack---to input on amp---to 16 ohm speakers.**

      Will a quality amp, tube or other, influence the quality, or is it already set by the phone's DAC?
      I only want to use the phone for it's interface to select my files to play.  I have read that any DAC connected to the phone's analogue earphone jack, ...will by-pass the phone's DAC?  This comment has been both substantiated and ridiculed, so I'm at a loss here.
      Seems to me that the earliest the quality is set, that anything after will just be upsampling.  
Is my most logical route to buy a DAC with a visual screen for file selection?

Any help here....would.....ah,!
Anytime you use the phone's analog outs, you are using it's own DAC.

Are you looking for portable music solutions, or for home? If the latter, consider a receiver with built in music streaming capabilities. :)
Not really looking for streaming, but want to play the hi-def music on my thumbdrives through a better DAC than the phone, but I will need one with a screen to select files, right?
I have an ongoing lack of understanding about what piece of equipment in the following system, actually gives the music it’s final quality out to my speakers.

Right. Well let me set you straight then. Every piece of equipment. Its that simple. Every single piece gives the music its final quality out to your speakers.
Will a quality amp, tube or other, influence the quality, or is it already set by the phone’s DAC?

Of course the amp has an influence on the quality- and regardless of the DAC.
Same goes for the wires connecting them.
Every. Single. Piece.
The signal source has the MOST affect on sound quality! You can't make a silk purse out of a ...
Power as in your ac lines has the most dramatic effect of everything. Address this first to get the most of everything that is plugged into it starting with your source wether it be ur computer, music server, dac, pre, amp, ect. ect.
You have no idea what you have unleashed sound22card :-)

Not that DACs in phones are "awful", but with the exception of a few LG models (and no doubt others), they are not very good either. There are some good DACs that connect directly to phone USB ports (not the headphone port).

Unless your source is "bad", usually the speakers in combination with the room has the biggest impact on your impression of quality. i.e. great speakers in a well designed room, connected up to a good DAC playing 320kbps MP3 and a reasonably good amplifier, is going to "sound better" than the worlds best DAC and amplifier playing high res audio through poor speakers in a poor room.  This is of course a generality, but for most people will be the case. 

Your impression of quality is usually first, is there something "bad" that irks you, and absent that, it becomes total presentation. Part of the "path" is eliminating really bad things from your system, and those bad things are different for different people. I could play $20,000 wonderfully clear and accurate speakers with an awesome system backing it up to someone who loves deep bass, and if those speakers do not have deep bass, they are going to hate it. Most electronics, even the DAC in your phone are usually not "awful" (emphasis on usually). Speakers can be awful. Cheap turntables can be awful. It's all relative. For many members here, if you said 320kbps MP3 could sound tolerable, they would look at you like you have 4 heads.
How many thumb drives do you have?  Can you put it all on a player like an astell & kern or even a Pono?  Other choice is put it all on micro sd cards (128gb) and put them in the phone.  Use an OTG cable ($5 on Amazon) to a real DAC.  Essentially you will put a ton of music on your phone, use the usb out to a DAC and from there to an amp.
So, essentially, the headphone 'out' of the phone gives me the phone's DAC result, but using an OTG cable, out of the phone's USB will allow a connected DAC to give me it's results....but this is how I access my music (thumbdrive through an OTG into the phone's USB).  I guess what I really need is a DAC that has a USB input, and a screen to view the files on the thumbdrives.
Thanks for the clarifications, folks.
My setup at the moment:

Laptop > 3.5/RCA > Vali 2 > recvr >   /Grado/Sony HP / B&W DM600 S3.

The quality of the 3.5/RCA really does matter. Amazon Basics, once you hear the difference, just no longer cuts it.

 I am on a *very* tight budget and have found used high quality cables/interconnects here for *very* good prices, mainly because I have no problem using gear that may be a few years old.

Regardless, enjoy the journey. If you let it, it can be a blast.
I read somewhere where an Android (Samsung) phone, the Galaxy 7, puts out 16 or 24 bits, at 48 or 192kHz ...only, ...through the headphone 3.5mm jack.  If my music is 32f bits at 96000Hz on my thumbdrive then it will be demoted by the phone's DAC, correct?  Wouldn't anything after that, even a high quality DAC only be able to deliver upsampled audio?....which defeats the purpose.  (No, I probably can't hear any difference between the two. That's not the point.)  I use an OTG cable to get the audio into the phone.  Is there a way to send audio into the phone to be able to select the files, and still get it back out to a good DAC without going through the phone's DAC?
Sisyphus' punishment...WAIT...not to roll the boulder up the hill...BUT down the hill.

No, I probably can't hear any difference between the two. That's not the point

DAC can be headless, but will need to have some streaming features. Look for those that have a respectable App. Control will be via Bluetooth or WiFi or both. 

Thumb drive into the DAC. Phone for App control.