The App is perfect for clicking copy/paste.

When you need to enter a password manually into a device not connected to the App, it sure would be nice to click a button to enlarge the field to full screen. Your only solution is to change the accessibility zoom or system font size. 

An example, on the Macintosh Contacts App, if you click on the phone number and select "Large Type", a grayed out box fills the width of the screen with the numbers as large as possible.