Is the iPhone 6 bigger than the iPhone 4 and 5?

Yes, the iPhone 6 screen is bigger. The iPhone 6 screen is 4.7" while the 5 is 4" and the 4 is 3.5".

Yes, substantially bigger. The iPhone 4 was 3.5 inches, the iPhone 5 was 4 inches, and then the iPhone 6 is 4.7 inches.