Help with 1820 VLAN configuration

[rydercowan]

I'm somewhere beneath novice status in networking, and would welcome some pointers. I have an 1820-8g switch serving a trunked NAS, a PC, and a VoIP adaptor. The switch has a port connected to a dumb switch with an Internet connection, which also serves another NAS.
Traffic from the NAS on the 1820 can be quite considerable, and I want to ensure that VoIP is not affected. I've read that segmenting with VLANs is good practice, and that ideally I should have a “VoIP” VLAN and a “Data” VLAN configured on the switch.
It appears that connected to the VoIP VLAN I need to have the VoIP adaptor, the PC (to manage the adaptor) and the port connected to the dumb switch, so I should have the relevant ports untagged in this VLAN definition. Connected to the Data VLAN I need the trunked NAS, the PC (to manage the NAS) and the port connected to the dumb switch. I also need to have the PC connected to the default VLAN, to manage the 1820. But I can't have the same port untagged in more than one VLAN.
I've tried setting ports as tagged in VLAN definitions, but that seems to leave the VLAN ID of the port set to the default VLAN.
I’ve spent hours grappling with this and I'm obviously missing something here, not yet having reached novice status, possibly connected with the difference between tagged and untagged ports. Help would be much appreciated with how I should configure the VLANs.

[16again]

Having a voice LAN also requires a different network  (IP addresses from different range) 
If your internet connection doesn't have separate port/VLAN for voice, there's hardly any use in setting up voice VLAN.