Most likely your front-end/UI uses other libraries to handle cross-browser issues so your automation tests will focus on the functionality of the application as opposed to catching cross-browser bugs or performance issues.
The problem that PhantomJS solves is to run headless browser which is very useful for organization that runs their build/tests on their CI-server and would prefer minimal setups (as opposed to have "testing-labs" like the big guys [yahoo, ms, google]). That itself reduces the cost of development/testing cycle.
Most likely your front-end/UI uses other libraries to handle cross-browser issues so your automation tests will focus on the functionality of the application as opposed to catching cross-browser bugs or performance issues.
The problem that PhantomJS solves is to run headless browser which is very useful for organization that runs their build/tests on their CI-server and would prefer minimal setups (as opposed to have "testing-labs" like the big guys [yahoo, ms, google]). That itself reduces the cost of development/testing cycle.