how do i download Xcloud for my phone if i already have Game pass ultimate

Xcloud is something different then. He would need a Game Pass Ultimate subscription. Then he would use the Game Pass app on his phone to use the Xcloud service.

I'm in a hurry to try it, I'll do some tests on my own.
I think coupling Xcloud and the Game Pass Ultimate would be really great!

Umm you do know that's already on right?

Two different services remote play on phones or xcloud which is a paid service with no console needed via gamepass ultimate

On pc or mobile

I have the Game Pass Ultimate since it came out and saw that xcloud came out so I installed and they told me to sign up, what I did my account is logged in but they ask me to buy the Game Pass Ultimate when I already have it active on my account. A solution
to offer me?

J'ai le Game Pass Ultimate depuis qu'il est sorti et j'ai vue que xcloud est sorti, j'ai donc installé et ils m'ont dit de m'inscrire, se que j'ai fait, mon compte est connecté mais ils me demande d'acheter le Game Pass Ultimate alors que je l'ai déj actif
sur mon compte. Une solution a me proposer ?

I had the same problem and found a solution. Before uninstall the app clear the cache and data in the App Settings of your device after that uninstall and reinstall the app. That's the only thing that let me log well into my Game Pass Ultimate account.

I'm honestly unsure how to help with the Nintendo Switch, but I do have an option for you. Right now there is a promotion for 3 months of Game Pass Ultimate for $1. You can put the Xbox (beta) app on a windows 10 or higher computer. Then download minecraft
and your son can play that way. Also you can try downloading Xbox Project Xcloud and try playing that way. I hope this helps!!!