You can configure your iPhone to automatically dial extensions. Here is how to do it:

1. Grab your iPhone and open the built-in Phone app.

2. If you need to create a new Contact, move to step 3. If not, find the contact you want to edit and tap it to enter edit mode. Then skip to Step 4 to add the extension.

3. On the Contact’s page tap the “add phone” label (it’s the “+” icon in the top-right corner of the Contacts screen) and enter the phone number that you want to call.

4. Tap the “+X#” key, then the “pause” option. This ads a comma to the phone number, which means that your iPhone will take a 2-second break before dialing the extension.

5. Now, input the extension and tap Done to save your changes. You can even add additional pauses and key presses if there are multiple options to navigate through.