Its not the plotting which fails, its your function M! Seems that you never tried to evaluate that function for single values.
1) In Prime a solve block is not created by writing "Given" - you have to insert the ugly looking block via the menu
2) You write m<=1 and m>=1. This would mean that you want m to be equal to 1 ???
3) What exactly do you want to minimize? Why is the first argument of minimize an "M"?
I guess that you just want to minimize phi but only with respect to the argument m and want Prime to use the provided values for T and H, right?
In Prime many things are broken compared to real Mathcad (you obviously try to duplicate a worksheet made in real Mathcad). So Prime would not allow partial arguments in functions.
This means that you will have to define an auxiliary function with only m as argument.
Did you had something like this in mind?
Prime6 sheet attached
