how do i install smime certificate on my iphone?

I am on the phone with Apple support trying to figure out how to properly install a freely downloaded Comodo S/MIME certificate on the iPhone. One the CA issues the certificate to my email, then I try to open the file for installation on the iPhone but the only option is to add it to iCloud.

S/MIME is turned on but I cannot add the certificate and Sign or Encrypt by default to turned on they are all grayed out.

Please help, this is a great security feature that we should be making use of but is quite tricky to set up. Maybe a release should be issued to make the installation process more streamlined you could team up with Comodo, Geotrust, or Symantec to issue these.