Final answer:
The number of bacteria on your phone after 4 hours is 81,000.
Step-by-step explanation:
To calculate the number of bacteria on your phone after 4 hours using the exponential function f(x) = 1,000 * 3^x, we can substitute x with 4. So the equation becomes f(4) = 1,000 * 3^4.
Calculating this, we get f(4) = 1,000 * 81 = 81,000.