Question regarding VOIP phones with passthrough ports and VLANs

So I've used this configuration a lot in my workplace, but since I'm not the one who administrates the network, I had a thought the other day and it started to confuse me.

So our network is set up to have a separate voice VLAN.

From the wall, the Ethernet cable connects to the LAN port of the phone, and then the workstation that the phone is sitting with is plugged into the PC port of the phone. Now, from what I understand, the phone essentially contains a three-port switch -- one for the PC, one for the phone, and one connecting to the switch in the server room.

Also from my understanding of networking, a port has to be trunked if it is to pass data for more than one VLAN. So, does the port on the switch in the server room that the PC and phone connect to need to be a trunk port for the link to the phone to be able to carry both voice and data? After all, if it essentially contains a 3 port switch, wouldn't the port need to be a trunk port on both sides in order to successfully pass data?

I've also heard that, for example, on Cisco switches, you can use a command to designate a voice VLAN on a port. So people will say, for example, that they have the voice data tagged for the voice VLAN via configuration on the phone, and then leave PC data untagged. I think here my understanding of VLANS starts to get shaky. How does this work? Does this essentially create a specialized trunk port that only allows untagged traffic and traffic tagged for one specific VLAN (the voice VLAN)? And also, perhaps where I'm getting tripped up -- is the untagged VLAN of a port specified on a port by port basis, or does it go for the entire switch? As in, does the switch have one cumulative native VLAN, or is the native VLAN designated separately on each port? If that's the case, I think I understand -- it doesn't matter what VLAN a PC is on if the untagged VLAN can be set to that whatever that PC's VLAN is, and then the tagged VLAN can be set to the voice VLAN. To further elaborate, if a switch port is set in access and NOT a trunk port, does it really just support a single "native" VLAN and that's it? If that isn't the case, I'm very confused.