This Blog Post should give you an easy to follow guide on how to set up an Exchange ActiveSync account on your iPhone or iPad.
Tap Mail, Contacts, Calendars
Tap Add Account
Enter your email address and your password that you use to login to your organisations network / computer with. Description can be changed to company name, making it easier to identify if you have a personal account already set up on the phone.
After Verifying, it may ask you to enter further details. You will need to enter the email address, username and password again. The Server address will need to be added also.
If you don’t already know the server address it can be found in Microsoft Outlook on your computer / laptop at work. This can be found by opening Microsoft Outlook > File > Account Information. the address will be under Access this account on the web. An Example would be https://outlook.company.com/owa to enter this address you will need to enter only outlook.company.com removing the https:// and owa
Entering the server address should verify the account and bring you to the option of what you would like to sync from your work account to your phone. You may wish to sync mail only.
You should now have your Exchange Mail, Contacts & Calendar synced with your iPhone.