Text field does not grow automatically.You have to use the textarea for that purpose
var win = Ti.UI.createWindow({
backgroundColor: 'white'
});
var textArea = Ti.UI.createTextArea({
borderWidth: 2,
borderColor: '#bbb',
borderRadius: 5,
color: '#888',
font: {fontSize:20, fontWeight:'bold'},
keyboardType: Ti.UI.KEYBOARD_NUMBER_PAD,
returnKeyType: Ti.UI.RETURNKEY_GO,
textAlign: 'left',
value: 'I am a textarea',
height:Ti.UI.SIZE,
top: 60,
width: 300,
});
win.add(textArea);
win.open()
Thanks