I'll answer my own question.
Must have an DDNS provider.
Go to “Features” > “Quick VPN” in router.
Turn VPN on. Change “User” & “Password” if you want.
Save file to Desktop which will be vpnprofile.mobileconfig.
Open the vpnprofile.mobileconfig file with Notepad (Windows).
Near the top, find:
<string>SharedSecret</string>
<key>SharedSecret</key>
<data>xxxxxxxxxx</data>
Write down the info between <data> & </data>. Case sensitive.
You will need this for the “Secret” password to install the profile later.
Near the bottom, find:
<key>UserDefinedName</key>
<string>DLink 880L</string>
Change the info between <string> & </string> to what you want, if not, Aaa will show up as your VPN name.
Save file, not “Save As”.
Attach this file and Email to yourself on iPhone.
Open this email on iPhone and click on the attachment.
Profile will start to install. Just follow prompts.
Go to “Settings” on iPhone and “VPN” should show up right below “Cellular”.
Click on “VPN” and you should see your VPN listed. Click button to connect or disconnect.
Works for me!