var PHONE_PRICE = 31;
var SPENDING_THRESHOLD = 23;
var bank_balance = 309;
var phone_accesory = 5;
var tax_rate = 12.5;
var total_amount = 0;
while(PHONE_PRICE < bank_balance){
  var gross_total = 0;
  if(phone_accesory < SPENDING_THRESHOLD){
    SPENDING_THRESHOLD -= phone_accesory;
    gross_total += phone_accesory;
  }
  gross_total += PHONE_PRICE;
  total_amount += add_tax(gross_total);
  bank_balance -= add_tax(gross_total);
}


console.log(pretty_print(total_amount));


function pretty_print(total_amount){
  return '$'+total_amount.toFixed(2);
}

function add_tax(gross_total){
  return gross_total * (1+tax_rate/100);
}