Should I download turbo tax on a computer or my iPhone? Does it make any difference?

You cannot use the CD/download on a phone or any other sort of mobile device.  The CD/download can only be used on a full PC or Mac.   If you only have a phone or mobile device, you will need to use the online software.

Thank you for your quick response. I’ll use the online format. I appreciate your help. 

Even if you use the "Online" software...it is easier to use on a computer. 

(yeah, true....that's just a strong personal opinion).

The issue I see with using a phone, is that people have to do a lot of scrolling just to see all the important stuff, and sometimes fail to do so.  Using the Online software on a computer, lets you see far more of the menu items all-at-once, even though a bit of scrolling will still be needed.

.......but your taxes are far too important to mess up.  Use your computer to prepare most of it.