A smartphone hasn’t been needed in the past, but it’s convenient.  When I did lab caches last year, the handout had the coords and the explanation of the task, you would write down the answers, and go to the website either right then on your smartphone, or later at home on your computer, and submit the answer.  See attached picture.  Notice that the website you need to go to for submitting your answers is shown near the top of the page.