Write an algorithm and draw a flowchart to calculate
2^4 using a loop approach?

I'm not about to write a flow chart for you, but here's a quick demo of how to do it:

doPower(2, 4);

function doPower(base, power){

   var result = 1, p;

   for(p = 0; p < power; p++){

       result *= base;

   }

   return result;

}

That function will only work for positive integer exponents of course.