Hi Dave,
1/1/12 should be trunk port, in traditional legacy world, phones are like switches so it understands tagging and Computers do not understand tagging.
Please send output of following commands:
show vlan brief e 1/1/12
show vlan brief e 1/1/48 (is it part of VLAN 70?)
Voice VLAN should be trunk/tagged data vlan should be untagged.
All you need to do is add as tagged port to both voice and data VLAN.
Then go to interface context and make sure you run command: dual-mode
Also check if 1/1/48 is port of both the voice and data VLAN.
If not then add to the ones missing in your config.
I think best is to open a TAC case and work interactively with our TAC.
Hope this helps.
Thanks
Hashim