Just for the posterity and somebody in the same situation;
I opened a case with ARUBA TAC and the conclusion is as follows:
-iPhone devices need the infrastructure certificate
installed via MDM or AppleConfigurator
Cannot installed the cert manually via downloading it from HTTP server.
So, even if your certificate is a legit one signed by a certificate authority,
if you do not install it on the iPhone device,
"Not Trusted" message will not disappear.
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