How to configure Dell 3548P to properly allow Cisco IP phones to register to Cisco VoIP PBX?

I have a Dell 3548P that I'm having issues getting configured properly so that the Cisco phones properly get DHCP addresses from my PBX.   Previously these were all working without issue when connected to Cisco 48 port PoE switches, but I've been tasked with making the environment work with 

The PBX is using VLAN100 for the Voice VLAN interface.  Right now all the ports on the 3548P are set as untagged VLAN1 (the default VLAN).  If I plug a regular laptop into a port on the 3548P, it gets an IP address properly which makes sense since the laptop would be using untagged vlan1.

However, it looks like the Cisco phones automatically want to use a VLAN100 tagged, so I supposed the obvious question would be, what should the configuration on the ports that connect any of the VoIP phones to 3548P, so that the switch will pass the VLAN100 traffic across the VoIP server, so that they get a proper DHCP address and register with the VoIP PBX?  

On Cisco switches, this tends to all come by default, but it looks like there's a bit more involved with trying to do it with a Dell switch.