How to make an anonymous function whose variable is itself a function of another variable?

Let's say i have an anonymous function defined in the following manner

z = @(x) cos(phi).^2 + 4*sin(phi).^2 and phi is defined in the following way

phi = @(x) x.^3 + 4*x.^2 + x +3

I have been trying to do this but when i call the function z in the following way, an error pops up

z(3)

Is something wrong in the syntax?

Answer 1

[Mischa Kim]

Salman, use

 phi = @(x) x.^3 + 4*x.^2 + x + 3;
 z   = @(x) cos(phi(x)).^2 + 4*sin(phi(x)).^2;
 z(3)
 ans =
   1.039526660425723

[Salman]

It worked! Thanks a lot.