Interpretation of Turing's statement on universal computers
To understand what Turing means here, you first need to understand what Turing means when he uses the word "computer". He is not talking about any particular machine, but about someone or something that 'computes', where 'computing' means to transform inputs into outputs according to some specification or function. 

The key difference between the everyday using of 'computer' and Turing's is the following: a 'computer' such as a pocket calculator or mobile phone consists of not only a 'computer' a la Turing, but also has an interface to this computer. Roughly, we can see this interface as a component that translates device input (touch screens, keys, etc.) to strings of 0's and 1's and translates this binary code back to device output (e.g. screen displays). This means that all the 'computer' has to do is compute on strings of 0's and 1's and leaves how to get input or present the output to the interface.



Now for the actual statement. What Turing says is the following:


If a computer can perform a certain (relatively simple) set of operations, we call it universal.
An universal computer can do anything another computer can do, given enough resources.


Part 1 should be clear. The 'resources' in part 2 is not very clear, but we can think a bit about what it means. Since a computer is something that only works with transforming binary code, the 'resources' of a computer are 'whatever is needed to perform this transformation on binary code'. What exactly are resources then depends on the type of computer: a mobile phone will need battery power to perform computations, while an engineer might be able to perform the same computations with a piece of paper and a good cup of coffee. Both of them will also need time to perform the computation.



We can now take a look at your calculator example. First of all, Turing's statement is only applicable if the simple calculators operations make it a universal computer. While a calculator is likely not universal, let's assume that it is for the moment. Then the computer 'inside'  the pocket calculator can do everything the computer 'inside' the graphical calculator can do, even though the graphical calculator can display things the pocket calculator cannot. 

What you should realize is that the difference in displays is a difference in interfaces of devices, not of their computers. The pocket calculator may not be able to show you a function plot on the display, but the display can certainly show the coordinates of all points on the plot.