A pass can only be on one phone. To move a pass to another phone, you need to contact customer service:

https://eurail.zendesk.com/hc/en-001/requests/new

You need to mention the pass number (from the confirmation mail or the Eurail account) and the start date of your trip.

They will then disconnect the pass from the phone, so it can be activated on another phone.

Quero transferir o passe do meu filho para o celular dele, como posso fazer isso? pois ele ainda podera usar na europa e eu ja voltei pro Brasil

You can use the Eurail pass in as many trains as you like. That can be anywhere, as long as the railway company operating the trains is covered by Eurail.

Ok, o passe eurail global pode ser utilizado em várias cidades dentro um país só?

As far as I know, there is currently no Portuguese version. There is a Spanish version, which should show up if you have Spanish as one of your languages in your phone.