Multi Selection Box User Submitted Values?

I'm currently having a problem with a multi selection box not taking user submitted values. I'm not sure if this is a limitation or just me missing something. I'll try to post enough pictures so you get the idea as uploading the entire file might not be possible. The box itself holds phase(s) with the default values being the most common. My main goal is to give the user the ability when he opens the combo box drop down to see his options, and if none of them fit his/her needs then give them the ability to input their own.

The Phase(s) default value are held in the "Multi-selection box" table

The Phase(s) information or whatever is selected while filling out the form goes to the "sub Table Information" table

The Phase(s) combo box itself is under the "Phase(s) & Effects" Form (subform) with "BSTS" being the main form