This page contains spoilers about the Heartbound ARG. If you want to solve the puzzle yourself, avoid reading this article.
Artifact 5

In the page's source you will see:

<!-- To leave this place... -->
<!-- Free me from this prison... -->
<div class="Do you agree...?">
    <!-- Up each step to the Theatre of Pompey. -->

Up each step to the Theatre of Pompey

A quick search should take you straight to Wikipedia. There we learn that it is famous for its steps, and for Julius Caesar being assassinated there.

So, clearly a variant of the Caesar cipher. In this case, the "up each step" part means that each letter has an increasing shift. With a little work, the shift tool will reveal the answer. Alternatively, a Vigenère cipher will work with the key "abcdefghijklmnop".

Regardless, the ciphertext decrypts to "ContractAccepted". Add that to the end of the URL, and you'll get to the final page of phase 2, the Sealed page.