The game is designed to fit within the size of your device's screen, meaning that the size of your game will be limited by the size of your device.
There is a feature in the Settings titled Customize Card Faces where you can change the font of your cards to be larger or smaller.
To select a new Card Face please open the game Settings, scroll down to the Customize Card Faces option and then select the option that fits your preference.
We also recommend rotating your device to play in Landscape orientation as this will make the cards appear a bit larger.