What's the best app to link Outlook and iPhone calendars together? Half of my schedule is linked to Outlook and the other is through my iPhone. Looking for an app or program that will feed one to the other and back.

This sort of thing is usually done via a CalDAV server. Multiple clients access a single server that hosts one or more calendars. Google is one provider, Apple's iCloud is another, there is free software that allows you to set up your own private server if you wish (assuming a certain amount of expertise). In other words, you have too many options to list, and probably already subscribe to a service that would facilitate this. Check the help pages for your cloud account providers.