Got it to work. Here was the process for others who are struggling.
Start with the desktop version of Joplin. After you have added some notes, select the Configuration menu. Select the Synchronization target. In my case: Dropbox. Then select the Enable Encryption option. It will open a form for a password. Enter a password. Write it down some where as you can't retrieve it...and you'll need it on your iPhone app. Exit the Configuration menu. You will get a popup asking your to save changes. Select "Save".
Then go to the Synchronization Option. You will get a page with a URL link to Dropbox. Sign in to your Dropbox account. You will get a page with the message that Joplin would like access to its own folder insider your Dropbox option. Select "Allow". It will generation along code# to enter into the Joplin App. Copy the code. Go back to the Joplin App and the paste code into the box then click on "Accept". You will get a pop up saying that the Authorization has succeed.
Let it synchronize. It will take a little while depending on how many notes and how much rich media are in the notes to copy all your notes to the Dropbox folder.
Now go to the iPhone app (I also set it up on my iPad the same way). On the upper left menu (three bars), click on Configuration> Synchronization
Select the Synchronization target from a dropdown menu. In my case: Dropbox.
Scroll down to "Encryption Config" and click on it.
Select "Enable Encryption", which open up a form to enter your password that you set up in the desktop app. Reenter it on Confirm Password box. Click on Enable.
Go back up to the Configuration menu. Select other things that will help you use it:
Being in the U.S. I selected the English (United States) language, the Date format option 01/30/2017 and the Time Format 8:30pm options.
You can also choose how ofter you want to synchronize your devices. I choose 5 minutes so the sync starts right away. You can go back and select a longer time period that uses less connection time later.
And you can choose Attachment download behavior. I use photos in my notes that are important content so I chose Always.
Once you are finished configuring, select the top left arrow to go back and you will get a box asking if you want to save changes. Select Save.
Now set up the synching with your existing Dropbox file from your desktop.
Go to the Synchronize Option at the bottom of the menu bar. Select it and you will go through the same process as you did on the desktop app. First you'll get a page with a URL link to Dropbox. Sign in to your Dropbox account. You will get a page with the message that Joplin would like access to its own folder insider your Dropbox option. Select "Allow". It will generation along code# to enter into the Joplin App. Copy the code. Go back to the Joplin App and the paste code into the box then click on "Accept". You will get a pop up saying that the Authorization has succeed.
It will then (assuming all goes well, as it did for me) sync your iPhone Joplin app to your desktop Joplin app and you will see your Notebooks and Notes populate on the left menu bar.