Yes, you can block iPhone IPSec on the ASA.
Try to connect the iPhone to the ASA, then on the ASA check the exact client type and/or version from the following:
show vpn-sessiondb detail full filter name
The output would include the Client Type and Client version.
From the Client Type and Client version, you can block it from the group-policy configuration:
ASDM --> Configuration --> Remote Access --> Network (Client) Access --> Group Policies --> Advanced --> IPSEC Client --> Client Access Rules --> Add --> Action: Deny --> VPN Client Type: from the above output --> VPN Client Version: from the above output
Hope that helps.