I don't think the iPhone can use the contacts in Outlook app.
However you can syncrhonize your contacts through iTunes :
- Connect your iPhone or iPod touch to your computer using the cable provided with your device or by placing the iPhone or iPod touch in the Apple Universal Dock
- iTunes opens automatically when connected to your computer.
- In iTunes, in the source list, under Devices, click the entry for your iPhone or iPod touch.
- Click the Info tab.
- Under Contacts, click Sync contacts from, and then click Outlook.
Or you can try to add your contacts in your iPhone :
Settings -> Mails Contacts, Calendar -> Add an account
And then just syncrhonize your contacts.