> Is this the most efficient way of doing it?

Sometimes the simplest solution is also the most efficient solution.  I'm not sure why you decided to use `Math.pow` and `PHI` to compute something that can be easily (and more quickly) be computed with simple addition:

<!-- language:lang-java -->

    public class EvenFibonacciFinder {
        private static final int MAX_NUM = 4_000_000;
    
        public static void main(String[] args)
        {
            long time = System.nanoTime();
            int  f1   = 1;
            int  f2   = 2;
            long sum  = 0;
    
            while (f2 <= MAX_NUM) {
                int f3;
                sum += f2;
                // This skips three ahead in the sequence.
                f3 = f1 + f2;
                f1 = f2 + f3;
                f2 = f1 + f3;
            }
            System.out.println("Result: " + sum +
                    "\nTime used for calculation in nanoseconds: " +
                    (System.nanoTime() - time));
        }
    }

Output:

> Original code using pow:  
> Result: 4613732  
> Time used for calculation in nanoseconds: 296694  
>  
> Using addition instead of pow:  
> Result: 4613732  
> Time used for calculation in nanoseconds: 45406