I's confused here... what is offering DHCP in the voice VLAN310, MiCollab? And MiCollab is at 10.32? And the 3300 is at 10.35?
If so, your option 125 is wrong... Actually I typically use Option 43 since it is an ASCII text option and easier to configure.
If your phones are already in the VLAN 310, you must not define tha VLAN tags, the phone will continue to request DHCP in the VAN specified in the DHCP offer until a DHCP offer is received with no VLAN ID specified, so it would look something like this:
id:ipphone.mitel.com;call_srv=10.127.10.35;sw_tftp=10.127.10.35;l2p=6;dscp=46
and that's it.
How are the phones getting to VLAN 310, via LLDP, Cisco SmartPort/Auto Voice VLAN, hard coded, or via a VLAN1 DHCP server offer?