"...there is no answer being produced for phi when I try to run the code"
There is. phi is calculated, and then that variable is never used anywhere: you do not display it nor return it as an output argument, so once the function gets to the end phi is simply discarded. But phi is calculated, just as you coded it to do.
Do you see the wavy orange and red underscores in the editor? You should pay attention to the messages that they have for you!
