Seems like the docs are all over the place on this, as I found this as well. Docs seem to contradict themselves. Not srue I follow what you mean about making voice vlan untrusted, specifically.
Tip: If you wanted to configure IP source guard on the voice VLAN as well as on the data VLAN, you would configure DHCP snooping and IP source guard exactly as you did for the data VLAN. The configuration result for the voice VLAN under secure-access-port would look like this:
secure-access-port {
vlan voice {
examine-dhcp;
ip-source-guard;
}
}