That's a different "All-New X-Men" to the "All New All Different X-Men". I'm not going to be ever be able to say that X-Men publishing is not confusing.
Indvidually, you'd want
Giant Sized X-Men #1
X-Men (1963) #94-137
There's not single digital collection of all of these issues.
If you link your Comixology account with Amazon, you can buy Kindle books on Amazon and read them on the Comixology app on the tablet, much cheaper with their current sale, but all these volumes are on both
X-Men Epic Collection Second Genesis (reprints Giant-Sized, #94-110 - same content as Marvel Masterworks Uncanny X-Men Vol 1 and 2 but half the price)
https://www.amazon.com.au/d/X-Men-Ep...J1F/ref=sr_1_1
Marvel Masterworks Uncanny X-Men Vol #3-5 (collects 111-140)
https://www.amazon.com.au/Uncanny-X-...313911-3228341
https://www.amazon.com.au/Uncanny-X-...313911-3228341
https://www.amazon.com.au/d/Uncanny-...OG2/ref=sr_1_9
Or just jump in and get just the Dark Phoenix story collection (#129-137)
(If you know generally who the major X-Men characters are you can pick it up and follow along, but as I said the story is the end to a longer story)
https://www.amazon.com.au/X-Men-Dark...313911-3228341