Is holding the mobile phone to read a post without scrolling considered a breach of an oath to refrain from opening a specific application?

Whoever swears not to do something and does not do it, does not break their oath and is not bound by anything. This is called an "oath of righteousness" (yamin al-birr), and the breaking of it occurs by voluntarily doing what one swore to abandon. Therefore, no expiation is binding upon you merely for taking your brother's phone and reading what is in it, because your oath was on not opening a specific application, not on not taking the phone or reading from it.