If you want to make your graph bigger, you can set your window to Fullscreen:
1) In the Graph window, tap the three dots in the upper right-hand corner.
2) Check "Fullscreen."
3) Pinch to resize the graph. You can also look at your graph as a landscape by rotating your phone as long as your phone as auto-rotate activated.
4) To exit Fullscreen, slide the top of the screen down as shown below.